Laars Mini-Combo II MCT User manual

Installation and Operation Instructions Document 8001D
H2077800D
FOR YOUR SAFETY: This product must be installed and serviced by a professional service technician,
qualified in hot water heater 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.
Installation and service must be performed by a qualified installer, service agency, or gas
supplier.
Installation
and Operation
Instructions for
Mini-Combo II
(Models MCT, MCS)
Residential Gas-Fired
Space/Water Heater
NOTE: This manual is to be used in conjunction
with Document 1025, Installation and Operation
Instructions for Mini-Therm II JV boilers.

Page 2 LAARS HEATING SYSTEMS
TABLE OF CONTENTS
SECTION 1.
General Information
1A. Introduction...................................................3
SECTION 2.
Installation
2A. Location........................................................3
2B. Heater Placement.........................................3
2C. Piping ...........................................................5
2D. Wiring ...................................................5, 6, 7
2E. Sequence of Operation ................................9

Mini-Combo II Page 3
SECTION 1.
General Information
WARNING
This manual supplies information on the application,
installation and operation of the indirect water
heater unit. A complete instruction manual of the
operation of the hydronic boiler (Document 1025) is
supplied along with this manual. Both manuals
should be reviewed completely before proceeding
with the installation.
• Failure to follow the instructions provided may
result in personal injury, death or substantial
property damage.
• Any modifications to the boiler, water tank, gas
and water connections, or wiring may void
warranty.
• Consult the factory or local factory representative
with any questions or problems regarding this
equipment.
Hazards and Your Safety
- Hot Water Can Scald!
Consumer Product Safety Commission and some
states/provinces recommend a temperature setting of
130°F (54°C) or less. The water heater thermostat is
factory set to approximately 120°F (49°C). If
thermostat will be set above factory setting, install an
anti-scald valve at either the water heater or at each
hot water faucet.
• Tempering valves are not anti-scald valves since
they do not have a positive shutoff in case cold
water supply fails. They are not recommended
for shower/tub service. If needed, install an anti-
scald valve at each shower/tub.
• Water heated to a temperature suitable for
clothes washing, dish washing and other
sanitizing needs can scald and cause permanent
injury.
• Children and elderly, infirm, or physically
handicapped persons are more likely to be
injured by hot water. Never leave them
unattended in a bathtub or shower. Never allow
small children to use a hot water tap or draw
their own bath. If anyone using hot water in the
building fits this description, or if state/province
laws or local codes require certain water
temperature at hot water taps, take special
precautions:
Install an anti-scald valve at water heater or at
each hot water faucet, bath, and shower outlet.
Use lowest practical temperature setting.
• Studies have indicated that dangerous bacteria
can form in potable water distribution system if
certain minimum water temperatures are not
maintained. Contact local health department for
more information.
SECTION 2.
Installation
This installation must conform with the
instructions in this manual and, where applicable:
Local, state, provincial, and national codes, laws,
regulations and ordinances.
In Canada - CAN/CGA B149.1 or B149.2
installation Code.
Where the recommendations made in this manual
differ from local or national codes, the local or
national codes take precedence.
2A. Location
This water heater/boiler unit is not intended for
outdoor installation. Select a convenient location
where water leakage from the tank or connections will
not result in damage to areas adjacent to the appliance
or to lower floors of the structure. When a safe
location cannot be found, install a suitable drain pan
under the appliance, and pipe it to an adequate drain.
2B. Heater Placement
The heater must be placed to provide clearances
on all sides for maintenance and inspection. Allow 4
inches (102mm) on each side for piping access. There
must also be minimum distances maintained from
combustible surfaces. Figure 2 shows minimum
clearance from combustible surfaces. The Mini-
Combo unit can be installed in a closet, as long as the
minimum clearances are maintained. Special attention
should be paid to the air supply opening to the closet.
Refer to Table 1.
Net Free Area - square inches sq. mm
Model Inside Air Outside Air
MC50 100 645 15 97
MC75 100 645 20 129
MC100 100 645 25 161
MC125 125 807 32 207
Area indicated is for one of two openings: One at floor level and
one at the ceiling, so the total free area would be double the
figures indicated. Refer to Document 1025 for more information
Table 1. Minimum Recommended Air Supply.

Page 4 LAARS HEATING SYSTEMS
B
54
1372
CVent Damper*
Tank
Relief Valve
Tank
Aquastat
Drain
Valve
24
610
A
CL
Hot
Water
Tank
Outlet
Inlet
28
711
FRONT VIEW SIDE VIEW
24
1
/
2
622
(Sizes 50 & 25)
25
635
(Size 75 & 100)
7
178
Mounted
Pump
System
Check Valve
Check Valve
Mini-Therm
Boiler
(50-125)
24
610
31
787
Boiler Approx.
MC A B C In/Out Gas Inlet/Outlet Weight
Size inches mm inches mm inches mm NPT NPT NPT lbs. kgs
50 58¾ 1492 12½ 318 4 102 1¼ ½ ¾ 258 117
75 58¾ 1492 12½ 318 5 127 1¼ ½ ¾ 274 124
100 59¾ 1518 14¼ 362 5 127 1¼ ½ ¾ 280 127
125 59¾ 1518 14¼ 362 6 152 1¼ ½ ¾ 286 130
Domestic
Figure 1. Dimensional Information.
Figure 2. Closet Installation.
7
178
Figure 4. Typical Expansion Tank Installation.
Figure 3. Piping Schematic.
Top Clearance
28
711
2
51
24
610
23 584
4 102
6 152
Dimensions
shown in inches
mm .
Cold
Water
Supply
Hot
Water
Supply
Minimum clearances from
combustible surfaces:
in. mm
left side 2 51
right side 0 0
rear 6 152
front 4 102
top 23 584
Service clearances:
allow 4 102 on each side
for piping access.
Space Heating -
Refer to Document 1025
Dimensions shown
in inches mm .
24
610
*Vent damper is optional on some Canadian units.

Mini-Combo II Page 5
2C. Piping
• To Prevent damage to the unit, all soldering is to
be done prior to assembling the cold and hot
water, and any other connections to the tank.
• Use suitable pipe dope or tape.
• Before piping the boiler to the heating system,
be sure to install the system check valve
(provided with the unit) onto the inlet (return)
tee of the boiler with arrow pointed downward
(see Figure 3).
• If anti-freeze is used in boiler system, local codes
may require a backflow preventer on cold supply
line. Use anti-freeze specifically intended for
hydronic heating system. Inhibited propylene
glycol is recommended.
WARNING
Do not use automotive or ethylene glycol anti-
freeze, or any undiluted anti-freeze. This can cause
severe personal injury, death or substantial property
damage.
If a backflow preventer, pressure reducing valve
or check valve is in cold water supply, install an
expansion tank on cold water supply line (Figure 4) to
prevent normal thermal expansion from repeatedly
forcing open the T&P relief valve.
T&P relief valves discharge piping must be
directed so that hot water flows away from all persons.
Attach run-off tube to T&P valve and run tube within
6" (152mm) from floor. No reducing couplings,
valves, or any other type of restriction is to be
installed in this line. This run-off tube must be
installed to allow free and complete drainage of both
valve and run-off tube.
Filling Storage Water Tank
1. Open hot water faucet in house to allow air in the
tank and in piping to escape.
2. Open shut-off valve(s) in cold water supply line.
3. Open shut-off valve(s) in hot water supply line.
4. When water discharges from the faucet, close it.
Check for system leaks and repair if necessary.
Filling and connecting boiler pipes:
Consult the JV boiler manual, Document 1025.
Caution
Never use water heater/boiler unless it is
completely filled with water.
2D. Wiring
Priority System: Under this wiring the storage
tank will be supplied before space heating. This will
insure that it gets adequate hot water flow from the
boiler to maintain a fully rated delivery of domestic
hot water.
Caution
In this priority mode, any demand for space heating
is postponed until the storage water tank has
reached set temperature. This delay in supplying
the space heating zones is usually not noticed by
the inhabitants of the living spaces. However, in the
event of certain storage water tank malfunctions,
space heating could be delayed indefinitely. If
undetected and uncorrected, freezing damage to
piping could result.
WARNING
Electrical shock can cause severe personal injury
or death. Disconnect power supply to the boiler
before doing any electrical work.
Electrical Connection: (See Figure 5, 6 and 7)
1. Remove the two screws attaching the front cover
of the control box.
2. There are five wires coiled in the area on the
right side of the control box, supplied with wire
nuts: 2 black wires twisted together, 2 white
wires twisted together, and a brown wire.
3. Follow Figures 5, 6 and 7. Remove the wire nut
from the two black wires, and connect the hot
lead from a 115 volt power supply to both wires.
Secure the three wires with the wire nut.
4. The two white, neutral wires should be joined to
the other neutral lead coming from the 115 volt
power supply, and the neutral lead coming from
the pump (space heating).
5. The brown wire attaches to the hot side of the
space heating pump.
6. There is a molex connector located on the left
side of the control panel. Connect the vent
damper harness to the molex connector and the
other end to the vent damper receptacle.
NOTE: The connection in step 6 should remain
intact at all times, otherwise the boiler will not fire.
Some Canadian units are supplied with vent
damper jumper plug. Do not remove jumper unless
vent damper is to be installed.

Page 6 LAARS HEATING SYSTEMS
H2001700H
THE BOILER WILL NOT OPERATE WITHOUT
THE AUTOMATIC VENT DAMPER. THE
VENT DAMPER WIRE HARNESS MUST BE
INSERTED INTO THE VENT DAMPER
RECEPTACLE
IN CANADA: SOME UNITS ARE SUPPLIED
WITH VENT DAMPER JUMPER PLUG. DO
NOT REMOVE JUMPER UNLESS VENT
DAMPER IS TO BE INSTALLED.
BK - BLACK
W-WHITE
R-RED
Y-YELLOW
BL - BLUE
BR - BROWN
O-ORANGE
P-PURPLE
G-GREENSPARK IGNITION WIRE
115V-FACTORY WIRED
115V-FIELD WIRED
24V-FACTORY WIRED
24V-FIELD WIRED
IF ANY OF THE ORIGINAL WIRE (AS
SUPPLIED WITH THE APPLIANCE) MUST
BE REPLACED, IT MUST BE REPLACED
WITH APPLIANCE WIRING MATERIAL
SUITABLE FOR 105 DEGREES C OR ITS
EQUIVALENT
GROUNDING
CONDUCTOR
115/60HZ
POWER SUPPLY
GAS VALVE
HW VR8300
PILOT BURNER &
THERMOCOUPLE
BR
SENSOR
BLOCKED
VENT
SAFETY
SWITCH
ROLL-OUT
SAFETY SWITCH
BK
BK
BL
BL Y
TH
TR
TANK
PUMP
BR
R
R
PUMP
(FIELD
SUPPLIED)
TANK
PUMP
RELAY
ZONE
PUMP
RELAY
HOT
NEUTRAL
24V
COM
SEN
NC
COM
NO
TANK
AQUASTAT
WALL
THERMOSTAT
(FIELD
SUPPLIED)
OPTIONAL
AQUASTAT HIGH
LIMIT VENT DAMPER
RECEPTACLE* TRANSFORMER
TERMINAL
STRIP
RO
Y
P
BR
R
P
R
R
Y
YG
24V 115V W
BK
BK
W
BK
BR
Y
Y
JUMPER BL
MODEL MCT
POWER VENTER
FAN PROVING
SWITCH
RECEPTACLE
SEE DOC. 1056
P
Y
W
Y
*
Figure 5. Wiring Diagrams.
H2001600J
PILOT BURNER
WITH SPARK
ELECTRODE
SENSOR
THE BOILER WILL NOT OPERATE
WITHOUT THE AUTOMATIC VENT
DAMPER. THE VENT DAMPER
WIRE HARNESS MUST BE
INSERTED INTO THE VENT
DAMPER RECEPTACLE
IN CANADA: SOME UNITS ARE
SUPPLIED WITH VENT DAMPER
JUMPER PLUG. DO NOT REMOVE
JUMPER UNLESS VENT DAMPER
IS TO BE INSTALLED.
IGNITION
CONTROL
1MV
2 MV/PV
3PV
4 GND
5 24V (GR)
6 24V
7 TH-W
8MV
9 SPARK
Y
BR
O
Y
GAS VALVE
HW VR8304
PV
MV
MV/PV
BK
BK
BK
SENSOR
BK - BLACK
W-WHITE
R-RED
Y-YELLOW
BL - BLUE
BR - BROWN
O-ORANGE
P-PURPLE
G-GREENSPARK IGNITION WIRE
115V-FACTORY WIRED
115V-FIELD WIRED
24V-FACTORY WIRED
24V-FIELD WIRED
IF ANY OF THE ORIGINAL WIRE (AS
SUPPLIED WITH THE APPLIANCE) MUST
BE REPLACED, IT MUST BE REPLACED
WITH APPLIANCE WIRING MATERIAL
SUITABLE FOR 105 DEGREES C OR ITS
EQUIVALENT
ROLL-OUT
SAFETY SWITCH
BLOCKED
VENT
SAFETY
SWITCH
POWER VENTER
RECEPTACLE
SEE DOC. 1056
BL
P
R
R
P
BR
R
RO
Y
YYG
24V 115V
Y
OPTIONAL
AQUASTAT HIGH
LIMIT VENT DAMPER
RECEPTACLE TRANSFORMER
TANK
AQUASTAT
24V
COM
SEN
NC
COM
NO
Y
RR
BL
BR
BR
BK
TANK
PUMP
PUMP
(FIELD
SUPPLIED)
W
GROUNDING
CONDUCTOR
115/60HZ
POWER SUPPLY
HOT
BK
W
BK
WALL
THERMOSTAT
(FIELD
SUPPLIED)
TANK
PUMP
RELAY
NEUTRAL
ZONE
PUMP
RELAY
JUMPER
TERMINAL
STRIP
R
W
A
BL
Y
MODEL MCS
Y
W

Mini-Combo II Page 7
Figure 6. MCT Schematic.
*
*Some Canadian units are supplied with vent damper jumper plug. Do
not remove jumper unless vent damper is to be installed.

Page 8 LAARS HEATING SYSTEMS
Figure 7. MCS Schematic.
*
*Some Canadian units are supplied with vent damper jumper plug. Do
not remove jumper unless vent damper is to be installed.

Mini-Combo II Page 9
Vent Damper Motor
Transformer
Figure 8. Sequence of Operation.
115 Volts Supply
Tank Stat
(common)
Domestic Demand
(N.C.) Heating Demand (N.O.)
Tank Pump
(energized)
High Limit
Switch
Vent Damper
Open
Power Vent
Fan Switch (optional)
Heating Pump
(energized)
Safety Limit
Switches
Main Gas Valve
(energized)
Boiler On
2E. Sequence of Operation

Page 10 LAARS HEATING SYSTEMS
Figure 9. Parts Identification.

Mini-Combo II Page 11
# Qty Part # Description
1 1 20085700 Weldment, Panel, Base
2 1 20085600 Weldment, Panel, Top
3 1 20086300 Weldment, Panel, Door
4 1 20086400 Panel, Side, Right
5 1 20127900 Weldment, Panel, Side, Left
6 1 20085900 Panel, Rear
7 1 20086500 Panel, Access
8 1 20084000 Bracket, Mounting, Left
9 4 20085400 Bracket, Support, Tank
10 2 P2015400 Tee, Blk, 1¼" x 1¼" x ¾" NPT
11 2 P0014400 Nipple, Black, ¾" NPT x 2.5" LG
12 1 P0014100 Nipple, Close, ¾" NPT
13 1 P2016900 Elbow, Blk, 90°, ¾" x 1" NPT
14 1 P0009300 Elbow, Street, Blk, ¾" NPT
15 1 H2078100 Label, Attention, Toxicity
16 4 P2014800 Fitting, Compress, 7/8" OD x ¾" NPT
17 1 P0008300 Elbow, Blk, 90°, ¾" NPT
18 1 A2085600 Valve, Check, ¾" NPT
19 6 ft. P2015000 Tubing, Copper, Type “L” 7/8" OD
20 1 A2085700 Valve, Drain, Tank, ¾" NPT
21 1 P0025300 Nipple, Brass, ¾" NPT x 2" LG
22 1 E0205000 Temperature Control, Electronic
23 1 A2085400 Valve, Relief, Temp & Pressure
24 1 A2085300 30 Gal Water Tank, Single Wall HX
1 A2085301 30 Gal Water Tank, Double Wall HX
25 2 Field Supplied Nipple, Brass ¾" NPT x 4" LG
26 1 Field Supplied Nipple, Brass 1" NPT x 3" LG
27 2 20087300 Door Latch Assembly
28 1 H2020600 Logo, Mini-Como II
29 1 H2016800 Label, Warning, Installation
30 2 H0090700 Label, Hot
31 not shown part not sold
32 56 F0024300 Screw, 10-16 x 5/8" LG
33 1 S0064900 Bushing, Nylon, Univ, 7/8" Dia.
36 1 A0066500 Pump, circulator, 1/25 HP
37 1 P0017100 Nipple, Close, Blk, 1¼" NPT
38 1 A2086600 Valve, Check, 1¼" NPT
39 1 H2017100 Tag, Important, Check Valve
40 1 A2087600 Handle, Door
41 1 H2017800 Label, Caution, Setting, Temp
42 2 A2086700 Flange, Pump, ¾" NPT
43 1 Vendor Supplied Well, Immersion, ¾ NPT
45 2 F0035900 Screw, #6-32 x 5/8" LG,
Phillips, Rnd Hd
46 1 Vendor Supplied Nipple, Brass 1" NPT x 2" Long
47 1 P0095000 Tee, 1" x 1" x ¾", Black Iron
48 1 P0071400 Plug, 1" Stainless Steel w/Vibroseal
49 1 20084001 Bracket, Mounting, Right
50 1 A2001500 Pump, Taco, 220V
51 1 E2103100 Sensor, Temperature
52 1 Q0068400 Tubing, Aluminum, 5"
53 2 F0035600 Nut, Speed, Push On
54 4¼ ft E0020900 Conduit, Flex, 3/8"
55 2 E0008300 Nut, Conduit, Lock
56 2 E0008100 Conduit Connector, 3/8"
57 5 E0007700 Wire Nut, 2 #4 Wires
58 4½ ft E0052500 Wire, #18 AWG 3/64", Yellow
59 4½ ft E0051900 Wire, #18 AWG 3/64", White
60 2 E0036100 Bushing
61 1 E0088400 Relay
62 1 E0097700 Relay, Case and Cover

H2077800D
Waterpik Technologies, Inc.
6000 Condor Drive, Moorpark, CA 93021 • 805.529.2000 • FAX [phone]
20 Industrial Way, Rochester, NH 03867 • 603.335.6300 • FAX [phone]
480 S. Service Road West, Oakville, Ontario, Canada L6K 2H4 • 905.844.8233 • FAX [phone]
www.laars.com Litho in U.S.A. © Laars Heating Systems 0009 Document 8001D