Monitor MZ Series Manual

2
MZ INSTALLATION & MAINTENANCE
The purpose of this manual is to provide a useful reference for
contractors, distributors, engineers, architects, building
owners, and those considering the use of this heating system.
1. There is no low temperature return limit. This means that
NO SYSTEM / THERMAL SHOCK PROTECTION IS
REQUIRED. The MZ is a fully condensing heating system.
The colder the return water, the more condensing action,
the more efficient.
2. The heat exchanger is stainless steel.
• You will not shock, warp, corrode, or otherwise harm it
with temperature or rapid temperature changes.
• No primary/secondary piping arrangements are needed
to protect the heating system from low-temp. operation.
• You can size the heating system to the heat loss of
the structure. This is important when the structure has
been improved over the years but the original radiation
remains, permitting lower operating temps at high
efficiency and comfort levels.
3. An adjustable control knob on the unit, from 65º to 176º F,
controls the outgoing water temperature limit for the main
I. INTRODUCTION - IMPORTANT INFORMATION
I. Introduction .................................. 2
MZ 25C
Important Information ...................... 2
The Monitor MZ .............................. 3
Technical Specifications ................. 4
Getting Started ............................... 5
Receiving, Opening, Storage ........... 5
II. Installation & Technical ............... 5
Location .......................................... 5
Mounting ......................................... 6
Using MZS to Produce DHW .......... 6
Condensate .................................... 7
Charging & Leak Testing ................. 7
Corrosion ........................................ 8
Freeze Protection ........................... 8
Gas Piping ..................................... 8
Propane Conversion ........................ 8
Venting ......................................... 10
Electrical . .................................... 15
Start Up ........................................ 16
Flow Verification ........................... 16
III. Accessories ................................. 17
BS Indirect Water Tank................. 17
Domestic Hot Water Kit ............... 18
MZ Mod Control ............................ 18
IV. Maintenance................................ 19
V. Troubleshooting ......................... 19
VI. Appendix A ................................. 22
Piping schematics ........................ 22
Wiring schematics........................ 26
VII. Appendix B ................................. 29
Parts and Assembly drawings ...... 29
VIII.Warranty ..................................... 40
! FOR YOUR SAFETY !
This product must be installed and serviced by a professional service
technician, qualified in hydronic heating system installation and
maintenance. Improper installation and/or operation could create carbon
monoxide gas in flue gases which could cause serious injury, property
damage, or death.
Improper installation and/or operation will void the warranty.
! WARNING !
If the information in this manual is not followed exactly, a fire or
explosion may result causing property damage, personal injury or
loss of life. Do not store or use gasoline or other flammable vapors
and liquids in the vicinity of this or any other appliance.
! WHAT TO DO IF YOU SMELL GAS !
• Do not try to light any appliance.
• Do not touch any electrical switch; do not use any phone in your
building.
• Immediately call your gas supplier from a nearby phone. Follow
the gas supplier’s instructions.
• If you cannot reach your gas supplier, call the fire department.
Products that have earned the Energy Star®are
designed to protect the environment through
superior energy efficiency.
ISO 9001 registered. Approved by AGA, CGA,
CSA, IAS, CE and several state and municipal
approvals.
TABLE OF CONTENTS - INTRODUCTION
heat. No other controls or mixing valves are needed for low
temp applications. The MZ’s design simplifies multi-temp,
multi-zone applications.
4. When using the MZ for domestic hot water (DHW) or other
priority application, use our MZ DHW kit, part # 9523. It
makes combining different temps for heat and DHW or
other applications quick and easy. Our 25, 40, 50 and 80
gallon BS tanks are perfectly matched to MZs.
5. MZ heating systems are completely self-contained.
Circulator pump, air eliminator, low water cut off, pressure
relief valve, condensate trap and drain, return water strainer,
temperature/pressure gauge, fill/ drain valve, on/off &
summer/winter switch, manual flow bypass, and, except
for the MZ40C, an expansion tank big enough for a 25
gallon system.
6. Three vent systems available:
1.) Parallel CPVC - separated exhaust & inlet air
2.) Horizontal concentric
3.) Vertical concentric
For most new and retro-residential jobs, there are no other

3www.monitorproducts.com
components to buy in order to supply heat to the distribution
system. The MZ is a “mechanical room on the wall.” Labor
savings are dramatic.
If a system is designed with a run temperature of 180°-200°F,
extra radiation may be needed since the MZ is not designed
for such high temperatures.
7. The MZ is wall hung, zero clearance, and direct vent (uses
no room air). It can be mounted almost anywhere; above
the washer / dryer in the laundry room, in a pantry,
bathroom, closet, kitchen - you name it. Because it has
no footprint, it is extremely valuable in condos and
apartments.
INTRODUCTION
8. MZ Heating System facts:
• Longest successful history of reliability of all high
efficiency, fully condensing heating systems.
• ISO 9001 certified.
• Perfect for radiant heating.
• EPA Energy-star listed.
• CSA Listed for Canada & US.
The rest of this manual should give you all the information
needed to properly plan, install, maintain and service this state
of the art, ultra high efficiency heating system.
Flame inspection port
(visible from cabinet door).
27-watt nearly silent air
inlet combustion turbine.
THE MONITOR MZ 25C
Heat exchanger exhaust outlet.
Adjustable system
water temperature control.
Condensate trap.
Heating system supply
water outlet from below
(connection in back).
System return water inlet
with stainless steel strainer
to prevent clogging.
Flue gas
outlet. Pre-mixing stainless steel burner.
Extremely
reliable spark
ignitor
Cast aluminum water jacket.
Stainless steel finned-tubed
heat exchanger.
Rubber gasket for
cabinet seal
Pressure relief valve.
Air Eliminator- NOTE: Air vent
on top is fully serviceable
without need to drain system.
Grundfos®1542 3-speed
circulator pump.
Electrical interface panel for
thermostat & household power.
Water proving flow switch.
Stainless steel fill &
drain ball valve.
Combustion air intake via
concentric flue housing.
Air flow proving switch.
Honeywell® gas valve.
Convenient tapping for
flue gas measurement.
System water
temperature/pressure indicator.
Gas inlet pipe.
On/Off switch.
Summer/Winter switch.
Expansion-tank NOTE: Easyoff
expansion tank connection.
(Typical of quick piping
connections and extremely easy
parts access throughout.)
Grommets for electrical wiring.

4
MZ INSTALLATION & MAINTENANCE
T E C H N I C A L S P E C I F I C A T I O N S
MODEL
BTU input
AFUE Efficiency
Built-in Controls
& Functions
Dimensions
Weight
Vent Length
Fuel (see pg. 12)
MZ25C
94,500 (Shown Above)
92 to 97%
(depending on return water temp.)
Priority pumped hi-temp
circuit (for DHW or heat)
30" H x 22" W x 13" D
125 lbs.
Vent runs longer than 13.5 feet derate input by 1% per 30 feet. Contact MPI if run is to exceed 30 feet.
Each MZ is factory tuned for natural gas, but propane kit is included. Conversion takes about 15 minutes.
MZ40C
71,000 / 142,000
92 to 97%
(depending on return water temp.)
Priority pumped hi-temp
circuit (for DHW or heat)
30" H x 22" W x 13" D
160 lbs.
MZ25S
94,500
92 to 97%
(depending on return water temp.)
Intergal DHW tank with
seperate aquastat
30" H x 22" W x 13" D
160 lbs.
QUICK REFERENCE INFORMATION
Heating value H
60°F / 5.5°C
BTU/foot3
CO/ CO2
Inlet Pressure (IWC)
Gas flow (cf per hour) @60°F
Air Reducer in /mm
Gas Orifice in /mm
P 2 (outlet pressure, IWC)
Air Pressure Switch Differential
Heat Input (BT_U / _HR)
MODEL
MZ 25
MZ 40
BOTH
MZ 25
MZ 40
MZ 25
MZ 40
MZ 25
MZ 40
MZ 25
MZ 40
MZ 25
MZ 40
MZ 25
MZ 40
MZ 25
MZ 40
NATURAL GAS
1075
30ppm / 9.5%
7.0"
87.9
132
1.14" / 29mm
None
0.228" / 5.8mm
None
2.8"
2.8"
1.57" IWC
.79" IWC
94,500
Two Stage
71,000 / 71,000 Each
LP GAS
2500
50 ppm / 10.7%
11.0"/13"
37.8
56.8
1.22"/31mm
None
0.138"/3.5mm
0.165"/4.2mm
5.50"
2.8"
1.57" IWC
.79" IWC
94,500
Two Stage
71,000 / 71,000 Each
MZ 25S Domestic Hot Water Flow Rate
Delta 54 °F (30°C) @ 2.91 GAL/MIN
Minimum System Water Flow Rate
MZ 25C and M25S: 3.5 GAL/MIN
MZ 40C 4.25 GAL/MN
Water Pressure
Heating pressure: maximum 43.5 PSI (3 bars) -
minimum 14.5 PSI (1 bar)
Hot water pressure: maximum 87 PSI (6 bars)
Maximum Operating Flow Temperature
Nominal 180° F (80° C).
Electrical Supply
120V -60Hz -15AMP
Combustion Products
MZ 25 SERIES: Max temperature: 176° F (80° C).
Flow rate 32° F (0° C) 14.7 PSI (1013 mbar):
1201 foot3/h - 34 m3 h.
MZ 40 SERIES: Max temperature: 176° F (80° C).
Flow rate 32° F (0° C) 14.7 PSI (1013 mbar):
2084 foot3/h - 59 m3 h.
Water capacity of expansion tank on MZ25C/S
26 gallon system capacity
Water capacity of:
MZ25C 1.5 gallons
MZ25S 6.50 gallons
MZ40C 2.25 gallons
INTRODUCTION

5www.monitorproducts.com
RECEIVING:
Before the contractor accepts the MZ, care should be taken to
verify that it has suffered no shipping damage. MPI cannot cover
shipping damage. Trucking companies refuse to cover hidden
damage if the damage is not claimed immediately.
The MZ is externally protected by foam inserts, a plastic bag
and cardboard corner braces. Between the foam protector for
the top of the MZ and the carton is a steel mounting rail that is
formed to match the mounting rail on the back of the MZ.
OPENING THE MZ:
The front cover of the MZ is sealed against the back with a
rubber gasket. With the cover on, the interior of the MZ becomes
a plenum. The cover is held at the top by a mounting lip from
which it hangs. The bottom of the cover is fitted with two clips
that snap closed around the bottom of the back. These clips are
secured with two screws that hold the clips in place. Remove
the screws so the cover can be removed. Replace them when
the installation is complete.
STORAGE:
If the MZ will not be installed right away it should be inspected
and then stored in a secure, dry location.
INSIDE THE COVER OF THE MZ ARE:
• Installation instructions
• LP conversion kit and instructions
• A container of BIONIBAL corrosion inhibitor
• A set of union elbows and gaskets for connecting the MZ
water and gas piping
• Two (2) service drivers.
You will notice that one of the heating systems “J” pipes has an
extra 3/4" male port on it. This can be used for the return of the
Domestic Hot Water or high temperature circuit, as well as an
auto fill valve if one is required or as the appropriate place to
connect additional expansion tank, if needed. If not needed, cap
it. If you are going to use it, check to make sure that the opening
in the male port has been drilled out.
All of the parts inside the MZ’s cover are important and should be
carefully guarded during the time between unpacking the MZ
and installing it. The gaskets that are part of the connection
kit are easy to misplace. Please put them in a safe place
until ready for installation.
GETTING STATED
CHOOSING A LOCATION:
When choosing a location to mount the MZ, run length of the
venting may be the primary factor, since it has the most limiting
factors and, in the case of the concentric type, it can be
expensive.
The other factors are proximity to existing or proposed piping
and gas lines, as well as a condensate drain. It is usually
easier to run longer piping and gas lines than it is to have a
far reaching and multi-elbowed vent system. The MZ should
never be mounted outdoors open to the weather. A sheltered
outdoor location is OK, but freeze protection of the condensate
trap and drain and of the circulating fluid will be necessary in
cold climate zones.
The mounting wall should be sound and dry. Wall anchors can
be used for masonry; screws for wood and carriage bolt for
metal frames. If the wall is stone or very uneven, a pair of 2x4s
from the floor to the ceiling joists works fine. Be sure to leave
clearance for the vent if vent is exiting straight out the rear.
Clean combustion air is necessary for proper operation of
MZ units. Some dust will be brought into the MZ and will burn
in the flame. Some of the ash produced will cling to the fins of
the MZ’s heat exchanger or be carried into the condensate
trap. Some airborne substances that can be encountered in
the residential and light commercial applications that the MZ
is commonly used in can cause premature failure of
components vital to the MZ’s function. The MZ’s combustion
air must be free of chlorine, fluorine, bromine, acids, cleaning
compounds, solvents, metal dusts, metal fumes and air
contaminated with the gasses produced in animal confinement
buildings.
Take special care to avoid chlorine fumes such as from
muriatic acid commonly used for concrete cleaning. Special
care should be given to MZ installations that are near
swimming pools, laundries, beauty parlors, dry cleaners, metal
working operations, metal treating operations, industrial
plants, automobile or diesel operations, and animal
confinement facilities.
The MZ is very quiet and is rated for zero clearance to
combustibles. It requires no special utility room or fireproofing
for its location. It can be put in living spaces, pantries,
bathrooms or closets. Since it is sealed combustion, it does
not need any indoor air source of any kind though indoor air
INTRODUCTION - INSTALLATION AND TECHNICAL
II. INSTALLATION AND TECHNICAL
Products
of combustion out
Combusion air in
Concentric flue illustrated here. Pipe must
be extended to outside of structure.
Combustion chamber Condensate collection

6
MZ INSTALLATION & MAINTENANCE
for combustion is approved if National Fuel Gas Code
requirements are followed.
Utilizing indoor air can cause a decrease in the overall system
efficiency. The MZ should not be run where ambient
temperatures exceed 125° F.
MOUNTING THE MZ:
The MZ comes from the factory with a wall mount bracket,
gas and water pipes. With this method you must: Mount the
bracket securely, hang the MZ, attach the included turn-down
elbows and begin piping. Note that when the caps that cover
the nipples on the heating system are removed, it is normal to
find water left over from the test-run firing at the factory. Watch
out for black-water staining if you are working in a clean area.
Always flush the heating system with plenty of clean water
before commissioning.
There are times when the rough piping for the heating system
must be installed and pressure tested before the heating
system is actually needed. The pre-plumbed wall bracket was
designed for this scenario.
Note that the pre-plumbed brackets come with and domestic
cold water shut-off valves on the 25S.
The pre-plumbed bracket (part #9511 for MZ25C pictured at
right, #9512 - MZ40C and #9513 for MZ25S) allows
completion of the heating and domestic water piping without
the heating system present. NOTE: All MZ heating systems
are shipped with an offset “Z” bracket for flush mounting. The
#9515 Spacer Back Plate for MZ25C & the #9516 Spacer Back
Plate for MZ25S and MZ40C allow piping to be run up behind
the unit.
Pre-plumbed brackets can be a big help with radiant systems
on new construction or major remodel jobs. Fit the bracket,
pipe the gas and heat, use standard pipe plugs with the
supplied fiber gaskets to pressure test the entire system.
When the time comes for the heating system, simply
remove the plugs, hang the MZ, tighten the union nuts
that connect the MZ to the piping and fill the unit. Pre-
plumbing spares you the worry (and cash flow) of having
the heating system sit on the job site out of your control
while construction goes on. Thirty minutes should be all
you need from delivery to light off.
USING MZS TO PRODUCE DOMESTIC HOT WATER:
a 54º F temperature rise. That is a constant draw of 174
gallons per hour. That setting maximizes efficiency and DHW
production, and works fine for a one-shower application.
The tank on the right side of the MZ25S inside its cover holds
system water. A copper fin-tub coil inside the tank transfers
heat from system water to domestic water. The adjustable
aquastat just above and to the left of the tank sets the limit
for the DHW-water temperature. We recommend a setting of
no more than 120°. If the DHW aquastat is set above 145º F
the fixed, manual-reset high-Limit supply-water thermostat
on the MZ may trip, causing nuisance callbacks.
The temperature of DHW is independently controlled and
regulated by adjustable settings on the MZ25S. The MZ25S
also includes an adjustable flow setting device for DHW.
When there is a low DHW flow through the MZ25S, the system
water in the tank will give up heat to the DHW and its
temperature will fall until the aqustat closes. The MZ will add
heat to the tank at faster rate than it is being taken out, and
the temperature in the tank and in the DHW will rise until the
aquastat is satisfied. Then the temperature will start to fall
again until the aquastat calls for heat again. This situation
presents little or no problem for laundry, dishwashing, hand
washing or other common DHW uses.
SIZING:
As long as the BTU output of the MZ is greater than the design
heat loss of the structure, the DHW draw on the MZ does not
have to be taken into account because DHW run times are
very short. The only time that DHW loads affect sizing is when
they are unusually large.
INDIRECT:
Because of its very high efficiency and very quick response
time, the MZ series is especially well suited for high-volume
DHW water production through the use of water storage tanks
using the heat produced by the MZ. Our 25, 40, 50 and 80
gallon stainless tanks are designed with the contractor, the
end-user and the MZ in mind.
In mixed space-heat DHW applications, the DHW function is
given priority over space heat through the use of a three-way
valve or priority pump system controlled to direct 100% of
the MZ’s output to the heat exchanger in the DHW system.
DIRECT DOMESTIC HOT WATER, THE MZ 25S:
The MZ 25S provides space-heat and DHW at extremely high
levels of efficiency and low levels of pollution. It is especially
well suited for structures in which floor space is at a premium.
The MZ 25S will produce 2.9 GPM of domestic-hot-water at
INSTALLATION AND TECHNICAL

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For steady water temperatures, the DHW water flow rate
through the MZ25S must be high enough to keep the MZ’s
burner on. If the user complains of DHW temperature swings,
especially in the shower, install a thermostatic mixing valve
between the hot and cold legs of the system. Make sure it is
a thermostatic, not a tempering valve. Also make sure that
the temperature setting of the MZ25S is at least 15° above
the desired mix temperature of the thermostatic valve (even
if it means a higher than needed gpm valve is used), or there
may be temperature fluctuations.
NOTE: The DHW performance of the MZ25S is not exactly
like that of a regular hot water heater, so make sure that you
or your customer understand its limitations. Filling a bathtub
will take longer, since most wide open spigots will not yield
hot enough water for a comfortable bath. The filling process
will have to be slowed in order to keep the temperature up.
Make sure your customer knows this! If space is not critical,
it is almost always better to use an MZ 25C and one of our
BS tanks. The cost of the tank and valves are little more than
the difference between the 25S and 25C. It has been our
experience that those people who choose the MZ25S do so
for the exceptionally high efficiency for overall DHW as
compared to conventional standing-pilot, gravity-vented gas
water heaters, and easily adjust to the subtle differences.
Table 1 may be helpful in balancing MZ25S DHW systems.
APPROXIMATE DHW PERFORMANCE OF MZ25S AT
VARYING FLOW RATES AND INLET WATER
TEMPERATURES. ALL TEMPERATURES ARE IN
FAHRENHEIT.
First column gives flow in gallon per minutes.
At any steady gallons per minute (GPM) flow rate, the MZ
will raise the temperature of the inlet water by a specific
amount. That temperature rise is shown in the second column.
Third, and subsequent columns, gives inlet water temperature
rising 5º F increments (top row) and the leaving domestic hot
water (DHW) temperature (remaining rows.)
GPM
1.5
1.75
2.0
2.25
2.5
2.75
3.0
3.25
3.5
3.75
Temp
Rise
105
90
79
70
63
57
52
48
45
42
35 F.
Inlet
Water
Temp
140
125
114
105
98
92
87
83
80
77
40 F.
Inlet
Water
Temp
145
130
119
110
103
97
92
88
85
82
45 F.
Inlet
Water
Temp
-
135
124
115
108
102
97
93
90
87
50 F.
Inlet
Water
Temp
-
140
129
120
113
107
102
98
95
92
55 F.
Inlet
Water
Temp
-
145
134
125
123
112
107
103
100
97
60 F.
Inlet
Water
Temp
-
-
139
130
128
117
112
108
105
102
Table 1
MZ25S Leaving water Temperatures, Degree F.
CONDENSATE:
Condensate removal can be accomplished by letting it drain
into the building’s normal drain or septic system. The MZ’s
condensate output depends on the return water temperature
of the heating system. Colder return water means higher
efficiency and more condensate. Over time condensate will
eat concrete, iron and copper drains. Most drain water is
alkaline which will neutralize condensate. Percolating
condensate through crushed limestone will neutralize it. If no
gravity drain available, an acid-proof condensate pump will
do the job.
CHARGING & LEAK TESTING:
It is assumed that the system into which the MZ is being
installed is a leak-free system. Leaks in the system will
damage the heating system and void the warranty. If there are
leaks in the system, fresh water will have to be added to the
system to replace the lost water. The addition of fresh water,
over time, will always bring air and dissolved minerals into the
heating system and will dilute the corrosion inhibitor. All of
which will cause a failure.
The proper concentration of BIONIBAL corrosion inhibitor (1%
by volume for all metal pipe systems and systems with oxygen
barrier tubing, 2% by volume for non-barrier systems) that is
shipped with the MZ will completely protect the MZ and the
system it is connected to from corrosion if kept at the right
strength. BIONIBAL does not deteriorate over time or get used
up over time. Additional Bionibal is available form MPI.
Once the system is properly charged with:
• Water
• BIONIBAL, or
• Water, glycol BIONIBAL mixture, it should remain stable
indefinitely.
Before the MZ is connected, the piping system should be
filled with clean, neutral P-h water to a pressure of 100 PSI. If
there is no change in pressure after 24 hours, the system
can be assumed to be leak-tight. The system should also be
visually inspected as thoroughly as possible. If any leaks are
found, they must be repaired.
The MZ has a brass, male-hose-thread, fill-and drain valve
operated by a stainless-steel ball valve. We recommend that
the MZ not be permanently piped to the structure’s potable
water system, unless local code requires auto fill. If auto-fill
is installed to the system, our recommendation is that it be
turned off. The flow switch in the MZ prevents low-water firing.
It is normal for heating systems to lose a very small amount
of water over time through valve stems or similar fittings. This
trivial amount of water can easily be replenished during normal
maintenance. There is a clear plastic tube in the MZ that fits
over the nozzle on the air vent and prevents the water that typically
spits out of the nozzle from staining the inside of the MZ.
On start up, the MZ should be run in the heating mode until
the entire system is brought up to operating temperatures.
Do not leave city water pressure on the auto-fill during normal
heating system operation since any system leaks will cause
the Bionibal corrosion inhibitor to be diluted and eventually
INSTALLATION AND TECHNICAL

8
MZ INSTALLATION & MAINTENANCE
eliminated. Oxygen and minerals in the water coming in to
replace the water leaking out will damage the MZ.
CORROSION:
The MZ should be filled with clean, clear, neutral ph water
suitable for drinking. A cleaning solution such as a mixture of
water and trisodium phosphate should be used in any systems
with oily residues. Many chemicals have been used over the
years in existing heating systems that could cause
premature failure of MZ units. It is important that no additives
be used in the system water for the MZ other than BIONIBAL,
which is supplied with each unit.
IMPORTANT: The use of a 2% by volume solution of
BIONIBAL in a radiant-heating system using non-oxygen-
barrier tubing will protect the MZ and the system to which it is
connected, from oxygen corrosion. In a system using tubing
with an effective, intact, oxygen barrier or in a hard-piped
system, a 1% solution of BIONIBAL is sufficient. BIONIBAL
doesn’t deteriorate or weaken over time, but should be
renewed if system is drained.
Under no circumstances should standard commercial anti-
freeze solutions be used in the MZ. Most of them contain
corrosion inhibitors that are not approved for use in the MZ.
They will cause heat exchanger failures that are not covered
by warranty. No other additives for lubrication, leak stoppage
or any other purpose can be used in the MZ. To do so will
void all warranty.
FREEZE PROTECTION:
In situations where freeze protection is a necessity. MPI ships
5 gallon quantities of BIONIBAGEL anti-freeze which is
formulated with Bionibal at a concentration that will bring a
50/50 mix of BIONIBAL and water to a 1% concentration of
BIONIBAGEL. If the application does not require a 50/50 mix,
the addition of sufficient BIONIBAL to bring the resulting
solution to a 1% concentration is important, otherwise bacterial
growth and corrosion may take place. In non-barrier systems,
which we discourage, a 2% concentration of BIONIBAL must
be assured. One quart (part # 9526) and 2.6 gallon (part
#9519) quantities of BIONIBAL are available from MPI.
Note that the addition of glycols to the water passing through
the MZ changes the rate at which the mix absorbs and
releases heat, decreasing its effectiveness as a heat transfer
fluid. Glycols also increase the viscosity of the water, making
it more difficult to pump. These factors can significantly
influence the overall performance of the heating system and
should be taken into account in the system’s design.
in an easily accessible place. The pipe supplying gas to the
heating system must not cause a pressure loss great enough
to decrease inlet gas pressure below the specified minimum
gas pressure values. (5" of water column for natural gas, 11"
for LP.) After initial start up, check that the pressure tapping
points are properly closed and check the general leak
tightness of the gas circuit. Always purge through the gas
pipe work before initial firing of the unit (in order to get rid of
any particles produced by welding or threaded joints).
The unit and its individual shut-off valve must be disconnected
from the gas supply piping system during any pressure testing
of that system.
NOTE: Many commonly used,
unapproved corrosion inhi-
bitors CAN DAMAGE THE MZ
AND VOID THE WARRANTY.
GAS PIPING:
The supply line is 3/4" NPT, and
enters at the lower left side of the
unit as shown.
The gas supply pipe must be fitted
with a 1/ 4 turn stop valve located
EXAMPLE PIPE SIZING TABLE
For gas flow through various pipe lengths and diameters.
(FOR REFERENCE ONLY)
Note: Table above is for natural gas with specific gravity 0.60
with a pressure drop through the gas piping of 0.30" w.c. Refer
to ANSI Z223.1 for additional pipe sizing.
Pipe length
(feet)
10
20
30
40
50
75
100
150
1/2"
132
92
73
63
56
45
38
31
3/4"
278
190
152
130
115
93
79
64
1"
520
350
285
245
215
175
150
120
1 1/4"
1050
730
590
500
440
360
305
250
Capacity of pipe for pipe size (ft3/hr)
NATURAL GAS TO LP GAS CONVERSION AND
HIGH ALTITUDE ADJUSTMENT:
Each MZ is supplied with a LP conversion kit. Follow steps
for conversion from Natural gas to LP:
1. Loosen the nut from the gas line/burner junction as shown on
next page (there are 2 on the MZ40C). Insert orifice into gas
line. Note that since there is no natural gas orifice in the MZ40C,
the tightening of the union between the gas line and the elbow
sometimes narrows the opening in the gas line for the orifice.
If that occurs, ream the opening. For MZ40C LP heating
systems, insert orifices before mounting heating system.
2. Reconnect nut and tighten.
3. For MZ25C/S models only: Remove the combustion air
fan by pulling it to the right. Disconnect the rubber air hose
and the wiring. Set the fan aside. Note: The split-ring LP
orifice slips into the burner, as shown below. If it fits loosely,
use the appropriate tool to open the split-ring LP orifice so
that it holds in place.
4. Inlet gas pressure for LP gas must be between 11" and 13"
water column with the heating system running. The MZ40C
requires no gas valve change. The MZ25C/S requires a gas
pressure adjustment from the factory 2.8" water column
setting to 5.5". The adjuster is under the slotted cap on the
gas valve. Turn the adjustment screw underneath the cap
full clockwise and then back off one turn counter-clockwise.
Replace cap. The heating system should then fire, permitting
outlet pressure measurement. Repeat adjustments until the
correct outlet pressure of 5.5" is reached. The final pressure
reading at tap P2 must be taken with the unit running and
the cap reinstalled on the gas valve.
INSTALLATION AND TECHNICAL
MZ
Heating
System
ÍGas Inlet

9www.monitorproducts.com
Important note about altitude: Since atmosphere thins
as altitude increases, there is less oxygen available to
support combustion at high altitude. The combustion-air
ALTITUDE ADJUSTMENT
1) Fire heating system. Let run for five minutes. Measure and
set CO at 30 PPM for natural gas (50 PPM for LP gas ).
There is a tapping in the vent elbow inside the MZ’s cabinet
just to the left of the flue-gas exit from the MZ for flue gas
measurement. Note that the cap that covers the gas valve’s
adjustment screw must be in place when CO measurement
is made.
2) Take cover off of air-pressure switch. With heating system
running, jump contacts so that heating system continues
to fire when switch opens.
3) Very, gradually block inlet air to blower with something light
and stiff, such as a credit card, until CO reads between
500 and 750 PPM. (NOTE: Blocking half of the blower
inlet may raise CO only slightly. As the critical point of
blockage is reached where CO does begin to ramp up, a
very small increase in blockage makes a very large
increase in CO. It is best to increase blockage VERY
slowly.) Remove jumper wire from switch. Burner will go
out and CO will begin to fall.
4) Adjust air pressure switch VERY, gradually counter
clockwise to the point where the switch closes, which will
then cause the burner to relight.
5) Unblock blower inlet air.
6) CO measurement should then return to 30 PPM for natural
gas ( 50 PPM for LP.) Check to verify that CO is normal.
7) Replace terminal cover on air-pressure switch, replace plug
in vent pipe, replace MZ cover. Cycle unit to verify normal
operation.
INSTALLATION AND TECHNICAL
blower used on the MZ
was designed specifically
for the MZ. Its normal
operating speed is partly
determined by the density
of the air moving through
it. As altitude increases,
the MZ’s blower spins
easier and faster in-
Combustion Chamber
unit pressure
Gas orifice is located in gas-line side of union. Spray union with penetrating
oil and tap wrench to locate nut on union. Gas line may need to be reamed
to accept LP orifice for MZ40.
Air pressure switch
Ionization probe
Outlet pressure
MZ25 Nat. 2.8
MZ25 LP 5.5
MZ 40 Nat or LP 2.8 Pressure
Tap P2
Gas
pressure
regulator
Servo-
system
Pressure
Tap P1
Solenoid
Inlet pressure
must stay within 5”
and 7” WC for
Natural Gas and
11” and 13” WC
for LP gas
Gas valve
To avoid pressure, remove cap, turn adjustment screw
clockwise to increase, counter clockwise to decrease.
Cap must be on to measure.
Ignition accelerator
Air fan
Ignition electrode
Air orifice location
Air pressure switch
test point
creasing the amount of air. The MZ can be used up to 6,000
feet dependinc on vent length of run, aAbove 6,000 feet,
adjustment of the air-pressure switch is necessary.
ALTITUDE
ADJUSTMENT
DIAGRAM

10
MZ INSTALLATION & MAINTENANCE
VENT KITS FOR MZ HEATING SYSTEM:
MINIMAL STARTER KITS
MP# Description Page No.
#9501 Horizontal Flue Kit, 1 Meter ................ 12
or
#9531 Vertical Vent Kit.................................. 14
HORIZONTAL CONCENTRIC BUILT-UP VENT
SYSTEMS
#9501 Horizontal Flue Kit, 1 Meter ................ 12
#9502 Horizontal Flue Kit, 2.5 Meter .................
#9503 Horizontal 90 ° Elbow ......................... 12
#9504 Horizontal 1 Meter Stick ..................... 12
#9520 Flue Adapter to Plastic Run................ 12
VERTICAL CONCENTRIC BUILT-UP VENT
SYSTEMS
#9505 Vertical Flue Adapter .......................... 13
#2206 Vertical Through-Roof Terminal 52" long
........................................................... 13
#2203 Vertical 1-Meter Stick ......................... 13
#2202 Vertical 1/2 Meter Stick ...................... 13
#2204 Vertical 45° “L” ................................... 13
#9031 Vertical 25-45° Roof Cooler................ 13
#9032 Vertical 35-55° Collar, Black............... 13
#9033 Pipe Support Ring .............................. 13
#9034 Vertical Black-Plastic Ceiling Trim ...... 13
#2205 Vertical 90° “L” ................................... 13
VENTING:
The MZ is designed for direct, concentric venting, although it
can be properly vented in other ways. The MZ is vented in 3
basic ways.
1. Horizontal Concentric
2. Vertical Concentric
3. Separated Exhaust & Inlet Air in 3" PVC
Horizontal vs. Vertical: The final terminal point of the vent
run determines which vent system should be used for the MZ.
THE SYSTEMS HAVE DIFFERENT DIMENSIONS AND
CANNOT BE MIXED. The horizontal system is less expensive
than the vertical system, foot for foot and fitting for fitting. For
vent runs in excess of 30 feet, contact MPI. All length of runs
must be accessible for inspection.
1. Horizontal Concentric:
The most economical venting location for the MZ is on or near
enough to an outside wall so that the vent box that fits the top
left-hand side of the MZ is within 38" of the final termination
point of the vent run. (see Fig. 1)
Use part number 9501 to provide all the necessary parts for
the above venting option.
The MZ’s horizontal vent system can run straight back from
the MZ or right, left, or over the top of the MZ at 90º increments
using the standard vent box mounting procedure. Vents must
slope back to the heating system. A minimum drop of 5/8th
inch per foot of horizontal run must be provided.
2. Vertical Concentric:
For vertical concentric venting, Monitor Products, Inc. kit
number #9505 is required. (see fig. 2).
Once the kit has been installed, the venting can be continued
by way of utilizing different lengths of concentric pipe, 90º
elbows, and 45º elbows. Part numbers & descriptions shown
in Table 1. Vents must slope back to the heating system. A
minimum drop of 5/8th inch per foot of horizontal run must be
provided.
TABLE 1
PART NUMBER CONCENTIC PIPE LENGTHS
2202 1.65 Feet (. 5 Meter)
2203 3.3 Feet (1 Meter)
2204 Vertical 45°
2205 Vertical 90°
INSTALLATION AND TECHNICAL
36”
Maximum
Minimum
6” clearance
Overhang is 2.5”
Intake pipe 1”
overhang
MZ Heating System
MZ Heating System
Fig. 1
Fig. 2
17.5” (.44 meter)
Intake adapter
Adapter and gasket

11 www.monitorproducts.com
After the area of termination has been selected use part number
#2206 and install vent termination utilizing support bracket
included with kit. (See Fig. 3)
3. Separated Exhaust & Inlet Air in 3" PVC
In a situation where it is desirable to route the venting in a non-
concentric fashion, use part #9530A as seen in Fig. 5. This kit
will allow for the exhaust to be piped independently of the
intake.
The venting then can be continued in 3" PVC for intake air,
and 3" CPVC for exhaust air. Termination then can be piped in
a conventional manner. Inlet and outlet should be in the same
wind plane.
The flue/combustion air system piping should be installed
observing the following criteria:
• For vent lengths in excess of 30 feet, contact MPI
• For each 90º elbow used in the flue system, subtract 3.3
feet from the total allowable length.
• For each 45º elbow used in the flue system, subtract 1.65
feet from the total allowable length.
• Horizontal runs of the flue system must pitch down 5/8"
per foot of length towards the heating system to facilitate
proper flue products condensate drainage.
• Termination of a horizontal flue system shall not be less
than 6 feet above walkway. Take care to minimize the
likelihood of flue/combustion air intake blockage. Vertical
flues must intake and discharge above the snow line.
• Do not place the flue terminal less than 3.3 feet from a
ventilation hole or opening in a building.
• Termination should be at least 2 feet above the snow line.
• All flue-piping components must be assembled to
provide an airtight flue/combustion air system.
INSTALLATION AND TECHNICAL
Termination of a
vertical flue must
provide at least 12
inches (30 cm)
above the roof jack
to the combustion air
intake collar. If there
are two units in the
installation with
vertical flue systems,
the termination of the
systems must be
separated by 16
inches (40 cm). (See
Fig.4)
s mmuusstt
9501 KIT FLUE
• BI-DIRECTIONAL VENT KITS: USE FOR TWO PIPE APPLICATIONS
• ALLOWS FOR 3" PVC VENTING
• THIS ARRANGEMENT CAN BE TERMINATED THROUGH WALL
LEFT, RIGHT, OR REAR
Fig. 5 9530A
3" Elbow, CPVC
Trim so that reducing
bushing fits snug on
top of box.
Bi-Directional box
Gasket
2.5" X 9 Long pipe CPVC
Locking ring
3" Coupling CPVC
4’ of 3" CPVC pipe
3" X 2.5" Reducing bushing
3" Male threaded apapter CPVC
Support bracket
(included with kit)
Fig. 3
Fig. 4 30 cm - 12”
Minimum
40 cm
16”
Minimum
mm
138.0
110.0
152.4
75.0
70.0
67.0
Inches
5.43
4.33
6.00
2.95
2.76
2.64
A
B
C
D
E
F
mini
Dimensions
6%
slope
back to
system.
5/8” per
foot of
run.
Intake pipe 1”
overhang
Air inlet 4.33”
(PVC dia. 110)
Flue gas outlet 2.95”
(PP dia. 75)
Drain slope towards inside 5/8” per foot Inspection hatch screw

12
MZ INSTALLATION & MAINTENANCE
The MZ can be supplied with a standard length flue,
which can be used to run through a wall up to three
feet thick directly behind the MZ. For greater lengths,
specify with your order.
HORIZONTAL CONCENTRIC VENTING: SHORT VENT RUNS
9051 Horizontal Flue Kit
HORIZONTAL CONCENTRIC VENTING: UP AND OVER LONG VENT RUNS
This arrangement recom-
mended for vent runs longer
than 4 feet.
Order lengths of 9504 to com-
plete desired vent lengths.
INSTALLATION AND TECHNICAL
PVC dia. 110
Dia. 4.33”
Positioning slot
Polypropylene dia. 75
Dia. 2.95”
This arrangement recommended
for vent runs shorter than 4 feet.
This arrangement can be termi-
nated through wall left, right, or
rear.
This end is final
wall termination
End view
(assembled)
Intake pipe - slides over exhaust pipe
39.36”
1 meter
MZ Heating System
9504 Exhaust pipe inside intake pipe
(cut length as needed)
9503 Exhaust elbow inside intake elbow
9520 Adapter and gasket
9501 Still needed for termination
DO NOT USE
* Note: Direct connection of # 9503
MZ Heating System

13 www.monitorproducts.com
9530A KIT FOR 3”
PVC VENTING
Existing chase used for flue and
intake-air runs (for instance,
chimney, after cleaning).
Continuous 3" PVC run for intake-
air is preferred, especially if very
clean chase cannot be assured.
DO NOT USE CHLORINATED
CLEANERS FOR CHASE
LEANING!!! Combustion air in.
Flue gas out.
Flue gas out
Combustion-air In
Combustion-air to MZ
Flue gas from MZ
Cap
Retaining ring Fits Inside of
Box to secure Bushing.
Combustion Air Inlet Bushing. Box to 3" PVC.
Combustion Air Inlet Run Can be 3" PVC.
3" X 3" CPVC TO
PVC Coupling.
Remainder of Flue
can be 3" PVC
3" X 4’
CPVC Stick
Top of heating
system to Top
of Elbow,
11.75”,
Minimum
3” CPVC Elbow
2.5” x CPVC Bushing
2.5” x CPVC Pipe. Trim so that Reducing
Bushing Fits Snug on Top of Box
Connection Box
Gasket Between Box and Heating System
All pipe 3" PVC. Connect to MPI’s accessory #9530
A, separated vent kit.
NOTE: Inlet and outlet must be
in same wind plane. Otherwise
they can be any distance above
grade or from each other as long
as flue gas cannot reach inlet and
as long as the entire system
meets the requirements of the
National Fuel Gas Code.
Exterior Wall
18” Minimum
Two Foot Minimum,
no Maximum
Soil or Snow Line
Foundation Wall
Combustion-air In
Products of
Combustion Out
CONCENTRIC FITTINGS FOR VERTICAL DISCHARGE VENTING
Polypropylene/PVC Concentric - Vertical
Terminal - For Flat or Sloping Roof
Extention - Joint Fitting
Useful length under sleeve tile - 16.9 inches
(0.43 m)
Concentric Fittings
Reference Color Length I.D. O.D.
2206 Black 42.5” 3.15” 4.9”
(1080mm) (80mm) (125mm)
Reference Length I.D. O.D.
2202 19.7” 3.15” 4.92”
(500mm) (80mm) (125mm)
2203 39.4” 3.15” 4.92”
(1000mm) (80mm) (125mm)
Useful length after assy. - 17.7 inches (0.45
m) [2202]or 37.4 Inches (0.95 m) [2203]
Polypropylene/PVC Concentric Elbow
-joint fitting
Reference Slope Covering Color
type
9031 25-45 deg Til Tile Red
9032 35-55 deg Slate- Black
Shingle
Sleeve Tile with
Adaptable Coupling
Reference Angle I.D. O.D.
2204 45 deg 3.15” 4.92”
(80mm) (125mm)
2205 90 deg 3.15” 4.92”
(80mm) (125mm)
Reference Diameter
mm
9033 4.92”
(125mm)
Fastening collar (each flue piece must
be adequately supported.)
Collare are essential to bear the weight of the
vertical extension.
Polypropylene Ceiling Plate to Cover
Rough Opening
Reference Color
9034 Black
INSTALLATION AND TECHNICAL

14
MZ INSTALLATION & MAINTENANCE
VERTICAL CONCENTRIC VENT
9505 Vertical
Flue Adapter
These parts are needed to fit the vertical-vent
system to the MZ. The internal flue pipe that ships
with the MZ is sized for the horizontal flue system
and side-by-side two-pipe vent systems. They are
used with the MZ more often than the vertical,
concentric vent system is. When the vertical-vent
system is used, the MZ’s inner vent pipe must be
replaced with one that matches the size used for
the vertical vent system
This Pipe
replaces
this pipe
MZ HEATING SYSTEM
MZ HEATING SYSTEM
9531 Vertical
Vent Kit
Pipe-support ring
Through-roof terminal
9505 (See above) and 9505 (See page 13)
MZ
HEATING SYSTEM
Intake
Pipe 1”
Overhang
6” Minimum
Slope Venting Back to System a
Minimum 6% Grade (5/8” per foot)
4.33” or (138mm)
Terminal must exit a
minimum of 18”
above the snow line
mandated by local
code or National Fuel
Gas Code.
INSTALLATION AND TECHNICAL

15 www.monitorproducts.com
ELECTRICAL:
• Electrical connections and control strategies, including
the summer / winter switch.
The installation must conform to one or more of the following,
as applicable:
A.) Local codes or, in the absence of local codes, the National
Fuel Gas Code, ANSI Z 223..
B.) Canada-CGA B149 installation code and/or local
installation codes.
C.) The National Electrical Code ANSI/NFPA No. 70.
D.) CSA Standard C22.1 and Canadian Electrical Code PZ.1.
ELECTRICAL CONNECTIONS FROM SITE
The heating system, when installed, must be grounded in
accordance with local codes or, in the absence of local codes,
with the National Electrical Code, ANSI/NFPA 70 and the CSA
Standard Canadian Electrical Code C22.1.
The MZ is designed for 120 volt, 60 cycle, three-wire (load,
neutral, and ground) current and draws about 112 watts in
full operation. The electric supply should be from a dedicated
15 amp circuit.
The MZ is easy to wire. Trim the minimum amount of material
from the pyramid-shaped grommets in the MZ’s cabinet so
as to provide a snug fit for all wiring in and out of the MZ. Run
low and high voltage wires through the strain reliever on the
left side of the control panel, through the chase and into the
control panel. Make sure polarity is correct or the unit will lock
out right after lighting.
There are 2 black jumper wires going into 3 terminals to the
left of the high voltage block. From left to right they are T3,
T2, & T1.
Note: If both jumpers are left in place, the pump will run
continuously and the MZ will maintain the aquastat
setting controlled by the adjustable black knob on the
MZ’s control panel.
Jumper position and the summer/winter switch have no effect
on a priority zone, or a Domestic Hot Water call coming in to
the MZ through the wiring harness that is part of the DHW kit.
If you desire constant circulation in the heating (winter) mode
(water moving through the “B” side of the 3-way valve at all
times if MPI’s DHW Kit is used for prioritizing or if the MZ 25S
is used) and the thermostat or heating system control firing
the burner as needed, then leave the jumper in T1, T2 and the
heating system control in T2, T3. Constant circulation has
multiple benefits. We recommend designing for constant
circulation whenever practical.
T3 T2 T1 N L
120V-60HZ
T3 T2 T1 N L
120V-60HZ
T
INSTALLATION AND TECHNICAL
Part 9520,
Flue Adaptor
to Plastic Run
Part 9504, Horizontal
I-meter Stick, Cut to
Length if Necessary
Part 9503,
Horizontal 90
Degree Elbow
MZ
HEATING
SYSTEM
Exterior Wall
Part 9501, Horizontal Flue Termination Kit, Cut to Length
Products of Combustion Out Terminal Must Exit at the Depth Above snow Line
Mandated by Local Codes of National Fuel Gas Code.
Combination Air In
Foundation Wall Above Grade
Notes: All flue parts are concentric. They exhaust
the products of combustion through a nominal 2.7”
pipe that is enclosed and supported within a nomi-
nal 4” pipe. The 4” conveys combustion air back
to the MZ.
All flue-pipe connection are gasketed slip-fit. It is
Snow Line
recommended that a lubricant such as soapy water be used to facilitate the slip-fit connection.
The male end of each connection should be inserted into the corresponding female end until it
bottoms out.
All flue components should drain back to the MZ.
The MZ an all of its flue parts are zero-clearance to combustibles.
If the terminal point of the MZ as shown in this drawing is below the local snow line, use appropri-
ate numbers of parts 9503 and 9504 to raise the terminal point. Local codes determine flue
distance above snow line. Always terminate with the terminal end of our 9051. Always terminate
in the horizontal plane. The horizontal system will not work in a configuration in which the termi-
nal end of part 9501 is in a vertical position.
Caution: The 24 volt transformer supplied
with the MZ is only intended to operate the
heating system components. If zone
valves are being used an auxiliary
transformer of the proper VA rating must
be installed separately. Please see zone
valve manufacturers data sheets for proper
transformer sizing and wiring
recommendations. Attaching zone valves
to heating system transformer will cause
damage and will void warranty.

16
MZ INSTALLATION & MAINTENANCE
T3 T2 T1 N L
120V-60HZ
T
To call for burner and pump at the same time, leave the jumper
in T2, T3 and the heating system control in T1, T2.
With the heating system’s summer/winter switch in the
summer (sunshine symbol) position, the heating system will
not respond to a call for heat from a space heat thermostat or
other space-heat control.
! AT T E N T I O N !
No attempt should be made to connect electrical
wires to any other location except
1. The indirect hot water storage tank wiring kit,
which plugs into the terminal socket on the right
side of the control panel cluster; and which also
includes strap-on aquastat to be installed inside
the MZ and wired in series with the MZ’s built-
in high limit flue and leaving water safety limits.
(See page 18).
2. Two-stage external control of MZ 20-40C.
NOTE: Two-stage operation of the Model MZ40C
is automatic: On a call for heat, both burners fire.
When return water temperature gets to between
9º F to 14º F of the setting on the adjustable
aquastat on the face of the heating system, the 2nd
stage shuts off and the 1st stage runs until the
heat call is satisfied. If return-water temp falls, the
second stage comes back on.
PREPARATION FOR USE/INITIAL START-UP:
Should overheating occur or the gas supply fail to shut off,
turn off the manual gas control.
Do not use this unit if any part has been under water.
Immediately call a qualified service technician to inspect the
unit and to replace any part of the control system or any gas
control, which has been under water.
Before initial start up of the unit, the installer should:
• Check that the gas circuit is leak free.
• Carefully flush out the gas pipes. Where the installation is
new, the purge serves to evacuate the air that is contained
in the pipes so that the unit has sufficient fuel. The presence
of air in the gas prevents the burner from lighting and results
in the flame control unit safety device cutting in. This applies
to a new installation running on either natural gas or LP.
For the latter, the storage tank must also be properly
flushed before initial start up.
ATTENTION! All necessary safety precautions should be
taken when venting the gas.
Flushing the gas will also have the effect of removing any oxide
particles from the pipes produced during brazing.
• Check that the flue outlet and air intake is leak free and
unobstructed.
• Check for the appearance of the flame through the round
observation window inside the hinged door just above the
controls.
• Check that the installation is filled with water. The water
pressure should equal 12 PSI.
The MZ heating system has two air purge valves, one on the
heating outlet, the other on the domestic hot water heater (25
S model dual-functioning unit).
• Check that the electricity supply is connected correctly:
120 V-60 Hz, with correct polarity.
• Check that the siphon trap is filled with water. Check that
the condensate outlet is connected.
• Make sure the circulator is running. If not, remove cap
covering shaft and manually start. The adjustable domestic
hot water thermostat is factory set on the MZ 25S. If it
becomes necessary to adjust this position it’s
recommended that for energy efficiency the setting be kept
at the minimum water temperature consistent with the
consumer’s needs. The maximum DHW temp is 145°. Keep
in mind there is a hot water scald potential if the thermostat
is set too high.
COMMISSIONING:
When operating the unit for the first time, the installer must
verify:
• That the gas valve works properly;
• That the flame control works properly;
• The burner setting: CO, CO2, and gas valve settings
are correct.
1. Open the manual valve on the gas inlet.
2. Switch on the main heating switch, or circuit breaker.
3. Set the lighted on/off switch on the control unit to the “on”
position.
4. Put the circulating pump switch to the “winter” position
(snowflake). In the “summer” position (sun), the circulating
pump only works when the domestic hot water tank
requires heating (MZ 25S or C models with indirect hot
water storage tank).
FLOW VERIFICATION:
In order for the MZ to function properly a minimum amount of
water must flow through the MZ’s heat exchanger to remove the
heat being produced. There is a flow switch inside the MZ that
will not allow the MZ to fire unless there is minimum flow.
Approximate external feet of head available from the Grundfos
UPS1542 in the MZ25 series heating system at flow rates shown.
GPM 3.5 4 6
Speed 3: FT of 12 10 5
Head Available
INSTALLATION AND TECHNICAL

17 www.monitorproducts.com
The pump in the MZ40C is generally not capable of pumping
normal heating zones outside the heating system. Such
applications normally will require additional series pumping or
a primary-secondary layout. The pump WILL supply adequate
flow for proper operation of one of our BS indirect tanks through
our DHW kit.
When the MZ is properly connected to a primary-secondary
pumping layout, the MZ’s pump will provide the necessary
flow. When the MZ is directly connected to a system in which
the pump inside the MZ is used to pump the entire system,
the system must be checked for proper flow.
If the system is a single-zone system or a multi-zone system
balanced with manually set circuit setters, there either will or
will not be sufficient flow to close the flow switch. If the system
is multi-zone with zone valves used to open and close zones
on demand, the system can be checked for proper flow by
running the system one zone at a time with all of the other
zones off.
If any of the zones restrict flow so much that the flow switch
will not close, adjustment to the system will have to be made,
such as wiring the system so that the restricted zone can
only operate when another zone is running or adding a pump
to that zone, increasing the pipe diameter or zone valve
selection for that zone, or installing a differential pressure-
overflow valve.
LEAVING WATER LIMIT-SWITCH FUNCTION
There is a manual reset high temperature limit switch in the
water jacket of the MZ. In systems with low flow or systems
with water-glycol mixes, it is possible for that manual reset
switch to trip before the call for heat has been satisfied. In
order to check for this possibility, the system should be run
with the adjustable limit switch on the MZ’s panel turned full
clockwise. The temperature - control devices in the system
(thermostats, aquastats etc.) should be adjusted to deliver
the highest temperature that this application will require until
those temperature-control devices are satisfied.
NOTE: If the system has been designed to require high
temperature (>176° F.) water at design conditions, care must
be taken to prevent nuisance trips of the MZ’s manual-reset
high-limit switch. The best ways to do that is to provide for
constant circulation in the winter mode, or add more radiation.
In multi-zone applications, each zone should be run
individually to assure that nuisance limit-switch trips will not
occur during the heating season.
If the manual reset switch trips, pull the adjustable-limit switch
knob and adjust the wire stops in the knob so that the
adjustable limit shuts the MZ down before the over-limit switch
opens. If the leaving-water temperature at that setting will
satisfy the structure’s need for heat on a design day, the
problem has been solved.
If the leaving-water temperature will not satisfy the need for
heat at that setting. Changes to the distribution system, piping
arrangement, pumping provision, control system, or the
addition of radiation may be appropriate. Do not install MZ
heating systems in jobs that require more than 176º F. water.
BS INDIRECT
WATER TANK
Models
Nominal Storage
Height
Diameter
All Pipe Connections
Max DHW Pressure
Aquastat Range
Aquastat Differential
Inspection Port Opening
Nominal Exchanger Power (170ºF Av. system Water Temp)
MZ25 Nominal Reheat Time from 50ºF to 140ºF Stored
MZ25 Continuous Output at 110ºF
MZ40 Nominal First Hour Draw at 70ºF Rise
Dry Weight
Gal.
IN.
IN.
MPT
PSI
F
F
IN.
MBH
MIN.
GPM
GAL.
LBS.
BS 25
25
27.5"
23.6"
3/4"
100
68-176ºF
10.8ºF
3.9"
115
10
3.8
250
71
BS 40
40
36.4"
23.6"
3/4"
100
68-176ºF
10.8ºF
3.9"
115
15
3.8
260
86
BS50
50
45.3"
23.6"
3/4"
100
68-176ºF
10.8ºF
3.9"
200
12
6.5
430
121
BS 80
80
63"
23.6"
3/4"
100
68-176ºF
10.8ºF
3.9"
210
17
6.7
465
159
E. DHW cold inlet.
F. DHW hot outlet.
G. Heating system
circuit inlet.
H. Heating system
circuit outlet.
I. Pressure-
temperature relief
A. 316 L austenitic
stainless steel coil.
B. 316 L austenitic
stainless steel tank.
C. Molded, rigid
removable insulation.
D. Removable ABS
plastic casing.
tap and/or DHW
recycling circuit
tap.
J. Inspection opening
and anode access.
K. Thermometer.
L. Aquastat.
Ratings assume cold-water inlet at 50ºF, heating system circuit average temp of 170ºF and heating system output at least
equal to the nominal heat exchanger power shown above. Tank output cannot exceed heating system output.
INSTALLATION AND TECHNICAL - ACCESSORIES
I I I . A C C E S S O R I E S

18
MZ INSTALLATION & MAINTENANCE
From Factory To 3-way To Indirect tank or
Harness valve motor High temp thermostat
Either black to Black
Either black to #2 on BS tank
Brown to #1 on BS tank
Orange to Brown
Grey to Blue
Green Ground terminal
(connect to ground) on tank
Red - not used
Red - not used
DHW KIT-MPI #9523
• Rapid way to offer two
temperatures
• Priority to DHW Zone
Monitor’s domestic hot water kit (part #
9523) allows for the zoning and control of
any indirect tank, or any two or more
temperature applications - one usually
being DHW recovery - with the higher temp
being a priority. This system utilizes the
built-in control feature that allows the non prioritized space-
heat side to be regulated by the main temperature knob and
the high temp side controlled by a strap-on aquastat.
The kit contains a factory wiring harness, 3-way valve, motor, and
strap on aquastat. The heating system output’s first connection
is the “AB” port of the 3-way valve. All system water flow thru the
“B” port will be controlled by the MZ’s main temp knob and the
heating thermostats. The “A” port will be the primary hi temp
circuit for DHW recovery. The “A” port is also a priority zone.
Wire the aquastat in series with the high limit on the MZ’s
water jacket. Strap the bulb to the leaving water pipe just
behind the combustion- air fan. Cover with foam insulation.
Secure with nylon ties; not ultra tight. Adjust leaving water
temp. at 170º to 175º F. Scratching the paint off the water
pipe will give a more accurate temp reading.
MPI #9110
MZ MOD CONTROL / MPI #9110
The MZ Mod Control comes with modulating control, 2 strap
on sensors, instruction manual, outdoor sensor, & wiring
harness.
Control Features:
• Versatile, easily adapts to all common piping methods.
• Heating system inlet and outlet sensors
• Optional primary loop sensor
• Optional DHW sensor.
• Smart control feature can adapt to the building.
• Exercising of heating system pump.
• Purging of heating system based on time.
MZ MOD CONTROL SPECIFICATIONS
Control — Microprocessor PID Control. This is not a safety (limit) control
Enclosure — Enclosure D, back Noryl Plastic
Optional Devices — Universal Sensor
Dimensions — 4-3/4" H x 2-7/8" W x 1-7/8 D (120 x 74 x 48 mm)
Approvals — CSA C US, meets ICES & FCC regulations for EI/RFI
Power Supply — 24 V 50/60 Hz 75 VA
Pump / Stage 1 Relay — 120 V (ac) 5 A 1/6 hp, pilot duty 240 VA
Stage 2 Relay — 120 V (ac) 3 A 1/6 hp
Alarm Relay — 24 V (ac) 3 A 1/6 hp
Ambient Conditions — Indoor use only, -40 to 140º F (40 to 60º C) <90% RH non-condensing
Sensors Include — NTC thermistor, 10 kW @ 77º F (25º C 0.2º C) B = 3892 2 of Universal Sensor and 1 of Outdoor Sensor
• Display of temperatures & run times
• Error messages for sensor failure with alarm signal.
• Minimum on and off delays
• Adjustable differential.
• Smart control feature adapts to each heating system.
• Built-in test sequence.
• Building occupants can be locked out of installer’s settings.
ACCESSORIES
Heating System Ground
MZ Heating System

19 www.monitorproducts.com
MAINTENANCE CONSIDERATIONS
The MZ is an extraordinarily durable and well-designed heat
source. It is built in the same manner as a fine boat or airplane.
While there are parts of the MZ that will eventually wear out,
they are easily replaced. The heart of the MZ, the heat
exchanger, is made of high-grade stainless steel and will last
for many, many years of normal service. Premature failure of
the MZ’s heat exchanger can be caused by the ingestion of
contaminant’s in the combustion air, the use of very hard, very
acidic or very basic water in the MZ, or continuous addition of
water to the system.
In order to minimize no-heat calls other than those that are the
unavoidable result of rare events such as a lightning strike or the
failure of one of the mechanical or electrical components of the
MZ, we recommend that the MZ be given an annual clean-and-
check. The few drops of water that will normally leak out of a
system over time can easily be replenished during maintenance.
If the MZ is not cleaned and checked regularly, there will
eventually be an interruption in the function of the MZ due to
one of the following, easily remedied events:
1) The air-pressure switch will not open due to a reduction in
airflow through the MZ due to an accumulation of dirt on the
inlet side of the combustion-air fan, the accumulation of dirt
in the burner, the accumulation of ash on the heat-
exchanger’s fin tube or the accumulation of ash in the
condensate trap.
2) The interference with ignition due to flame erosion of the
igniter rods.
Annual service will bring the chance of nuisance no-heat calls
to near zero.
MAINTENANCE PROCEDURES
(Approximate time, 15 minutes.)
1) Disconnect plastic tube at top of fan. Grasp plastic nozzle
that connects fan to the burner with right hand. Rest left
hand on combustion chamber and pull fan to right. Fan will
slip off of burner. Disconnect fan wiring connector and set
fan aside.
2) Disconnect plastic hose, igniter wire, flame-proving wire
and ground wire from burner top. Open union in gas line at
burner top. Four bolts secure clips that hold burner to
combustion chamber. Remove front clips. Loosen bolts and
rear spin clips so that burner can be removed and remove
burner.
3) Using plain water, wash heat exchanger fin-tubes. Water
will run out through condensate trap. Unscrew bottom half
of condensate trap. Check trap for accumulation of ash/
mud and clean if necessary. Fill the trap with water and
replace it.
4) Inspect flame proving rod and igniters. Replace if worn. Re-
gap igniter according to specifications in the Technical
Instruction packed with heating system. (2.25 mm, 0.09
inches.) Brush or vacuum burner face. If vacuum is at hand,
vacuum burner outlet. Check fan inlet for dirt on blades and
clean if necessary. Re-connect burner, hoses, wiring, and
fan.
5) Fire MZ, check safety limits and CO and/or CO2 according
to values in installation instructions.
QUICK TROUBLE-SHOOTING GUIDE FOR MZ
HEATING SYSTEMS:
!WARNING!
Only trained HVAC service people should do MZ
troubleshooting. The MZ is fed by an electrical current
source that could electrocute. Take care to avoid shock.
Wear safety glasses!
Make sure that the MZ has power, gas, that there is water in
the heating system and that there is a call for heat. Check all
visible hoses and wiring inside the MZ for integrity and good
connection.
Is pump running?
Toggle on-off switch. Water pressure will change when pump
starts. If no change, remove cap from pump end. Rotate shaft
with screwdriver. If shaft rotates freely, check power to pump
(CAUTION, 110 VOL TS). If no power to pump, check pump
relay and associated wiring.
Fan runs but MZ doesn’t try to fire?
Check for air-pressure-switch operation with voltmeter. If
switch does not close, check for blocked flue, blocked
condensate trap or drain. If MZ has been in service for a long
time, make sure that heat exchanger is not dirty. Inspect
venting to insure compliance with installation instructions.
Is water-flow switch closing?
Disconnect flow-switch wiring-harness. Jump connections
back to MZ. If fan runs with connections jumped, most likely
cause is low system water flow. Check for stuck valve,
obstruction in piping, strainer or pump vanes clogged, etc.
Use ohmmeter to check for flow-switch operation. Switch
closes at 3.52 GPM for the MZ25 and 4.4 GPM for the
MZ20-40.
Does the MZ try to fire?
Gas valve and spark normally act simultaneously about 20
seconds after air pressure switch closes. If attempt to light
occurs, but no flame results, (flame failure), the ignition module
will lock out, the fan runs continuously, and power has to be
interrupted before another attempt to light will occur.
Is combustion-air fan running?
If pump runs and flow switch closes, combustion air fan should
run. If not, verify call for heat, check that operating limit is not
satisfied and that manual reset fixed high-Iimit switches are
not open. If fan does not run, check fan power (CAUTION,
110 V.). If no power, check fan relay and associated wiring.
MAINTENANCE - TROUBLESHOOTING
I V. MAINTENANCE
V. TROUBLESHOOTING

20
MZ INSTALLATION & MAINTENANCE
Is there flame failure?
Likely flame failure causes: bad gas-air mixture (too little or
too much gas), no spark, reverse polarity or poor ground.
Check spark by looking up into sight glass at sharp angle.
Check for proper gas pressure with manometer. Check power
for grounding and polarity with volt-amp meter. Check ignitor
electrode gap.
Proper gas-air mixture plus spark equals ignition. If you don’t
have ignition at this point, re-check everything.
When you realize that the MZ is a heating system that requires
nothing more than certain occurrences in sequence to operate,
troubleshooting becomes very straightforward. There are no
circuit boards (other than what may be in the Honeywell flame
control module), only a few relays that dictate exactly what
the MZ is doing, and if it not working, what it needs to do.
Here is the sequence of events that occur during normal
operation:
1. Power on to the unit
2. Call for heat - both T1, T2, & T2, T3 circuits must be closed
or there must be a DHW or other priority call.
3. Adjustable limit, leaving water and flue limit switches
closed.
4. DHW aquastat closed if priority call.
5. Fan full speed.
6. Pressure differential switch must close.
7. Gas valve open, spark.
8. Flame module proves flame and keeps gas valve open
until high limit is reached, DHW aquastat is satisfied or
call for heat is over.
Other than those sequential steps, there is nothing else that
affects the MZs operation. Here is a troubleshooting chart:
PROBLEM
MZ not running.
Power switch
not lit.
Power on,
nothing
happening.
No heat or
hot water.
Call for main
heat or priority
heat has been
verified. All
limits are
closed. No fan.
Pump is
running, fan is
running, unit
won’t fire.
POSSIBLE CAUSE
1. Power turned off, breaker off.
1. Check for high limit trip on top of heat
exchanger or where flue exits at bottom.
2. Check that adjustable operating limit is closed.
3. Make sure there is a call for heat or hot water.
4. Transformer failed.
5. Make sure pump is running (this can be done
by feeling for vibration or turning switch off and
on and watching for movement in the pressure
gauge).
1. No water flow through the unit. Not enough
flow to satisfy switch. Air in the system, or
return water strainer clogged.
2. Obstruction to flow outside MZ (such as stuck
zone valve).
Check position and integrity of tubes at air pressure
switch. Make sure that tubes are not cut anywhere.
Long tube from fan should see greater than 1.9
inches of water column and should be connected
to + (plus) port on switch. If p is less than 1.9, clean
and check fan.
If the pressure difference between the tube from
the fan and the tube from the combustion chamber
is greater than 1.6 inches of water column (IWC)
for the MZ25 or greater than .9 IWC for the MZ40,
the switch should close.
If pressure switch is OK, after blower has reached
full speed, switch should close. About 20 seconds
later, gas valve should open (loud click) and spark
should commence (spark visible through sight glass
when viewed at sharp angle from below).
REMEDY
1. Restore power.
1. Push to reset. If this occurs regularly, see below.
2. Check thermostat, jump T1, T2 & T2, T3. Make
sure switch is on winter (snowflake)
3. Check wires
4. Check for voltage on 24V side, replace if none.
5. Check for power to pump with tester and / or listen
for second relay from left to engage when power
is on. If there is power but no movement, remove
the silver slotted screw from the pump body and
turn the shaft manually. If the pump starts, replace
the screw. If it turns easily, replace the pump.
1. Jump red & orange wires to flow switch. If unit
starts and runs normally, either flow switch is bad
(unlikely) or there is no or low flow.
2. Find and clear flow obstruction. To clean strainer,
remove large nut behind fill/slash drain valve and
pull out strainer. Clean or replace.
Listen for click for gas valve relay after fan has
reached full speed. Watch for spark thru glass in
chamber. (If there is no click or spark, remove the
short clear hose from the black pressure switch. If
the unit fires, the venting is restricted. If no change,
jump the switch. If unit doesn’t fire after 30 seconds
of full speed fan operation, replace Honeywell control
unit. If there is a click but no spark, test for 110 volts
to spark transformer. If there is voltage, test for high
voltage with spare igniter. No high voltage, replace
transformer. If there is high voltage, replace igniter.
If the gas valve clicks and the igniter sparks, remove
P1 on the gas valve a make sure there is gas to the
unit.
TROUBLESHOOTING