Mod Con 300 User manual

nWARNING
This manual must only be used by a qualified heating installer/service technician. Read all instructions
in this manual before installing. Perform steps in the order given. Failure to comply could result in
severe personal injury, death or substantial property damage.
Installation
Manual
• Installation
• Startup
• Maintenance
• Parts
Installation
Manual
• Installation
• Startup
• Maintenance
• Parts
NOTICE
Heat Transfer Products, Inc., reserves the right to make product changes or updates without
notice and will not be held liable for typographical errors in literature.

1
GAS-FIRED BOILER Boiler Manual
WARNING
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 neighbor's 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 the gas supplier.
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.

GAS-FIRED BOILER Boiler Manual
2
CONTENTS
Part 1 – Product and Safety Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6
Part 2 – Before You Start. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7
A. What’s In The Box
B. How The Boiler Operates
C. Optional Equipment
Part 3 – Prepare Boiler Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-12
A. Boiler Location Should Be Level
B. Installations Must Comply With:
C. Before Locating Boiler
D. Clearances for Service Access
E. Residential Garage Installation
F. Exhaust Vent and Intake Air Vent
G. Prevent Combustion Air Contamination
H. When Removing a Boiler from an Existing Common Vent System
Part 4 – Prepare Boiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-13
Part 5 – Boiler Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-23
A. Relief Valve
B. General Piping Information
C. Backflow Preventer
D. System Water Piping Methods
E. Circulators
F. Hydronic Piping with Circulators, Zone Valves and Multiple Boilers
G. Boiler Piping Details
H. Circulator Sizing
I. Fill and Purge Heating System
J Zoning with Zone Valves
K. Zoning with Circulators
L. Multiple Boilers
Part 6 – Venting, Combustion Air & Condensate Removal . . . . . . . . . . . . . . . . . . . . . 24-34
A. Installing Exhaust Vent and Intake Air Vent
B. General
C. Approved Materials for Exhaust Vent and Intake Air Vent
D. Exhaust Vent and Intake Air Vent Pipe Location
E. Exhaust Vent and Intake Air Vent Sizing
F. Longer Vent Runs
G. Exhaust Vent and Intake Air Pipe Installation
H. Heater Removal from a Common Vent System
I. Diagrams for Sidewall Venting
J. Diagram for Vertical Venting
Part 7 – Gas Piping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-39
A. Gas Connection
B. Gas Piping
C. Gas Table
D. Check Inlet Gas Pressure
E. Dungs Gas Valve

GAS-FIRED BOILER Boiler Manual
3
CONTENTS (CONT’D)
Part 8 – Field Wiring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40-48
A. Installation Must Comply With
B. Field Wiring
C. Line Voltage Wiring for Standard Boiler
D. Alarm Connections
E. Low Voltage Connections for Standard Boiler
F. Thermostat
G. Outdoor Sensor
H. Indirect Sensor
I. Optional 0-10 Volt Building Control Signal
J. Optional High Gas Pressure Switch
K. Optional Low Gas Pressure Switch
L. Optional UL353 Low Water Cutoff Switch
M. Wiring of Cascade System Communication Bus
Part 9 – Start Up Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49-52
A. Check/Control Water Chemistry
B. Freeze Protection (when used)
C. Fill and Test Water System
D. Purge Air from Water System
E. Check for Gas Leaks
F. Check Thermostat Circuit(s)
G. Condensate Removal
H. Final Checks Before Starting Boiler
I. Cascade System
Part 10 – Start-Up Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52-54
A. Operating Instructions
B. Adjusting the Set Point
C. Status Menu
D. Test Mode
Part 11 – Start-Up Procedures for the Installer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55-57
A. Programming for the Installer
B. Program Access
C. Program Navigation
Part 12 – Troubleshooting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58-61
A. Mod Con Error Code
B. Boiler Error
C. Boiler Fault
Part 13 – Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61-71
A. Maintenance Procedures
B. Combustion Chamber Coil Cleaning Instructions for Mod Con 300/500 Only
Inspection and Maintenance Start-Up Charts

GAS-FIRED BOILER Boiler Manual
4
PART 1: PRODUCT AND SAFETY INFORMATION
SPECIAL ATTENTION BOXES
The following defined terms are used throughout this manual to bring attention to the presence of
hazards of various risk levels or to important information concerning the product.
nDANGER
DANGER indicates an imminently hazardous
situation which, if not avoided, will result in
death or serious injury.
nWARNING
WARNING indicates a potentially hazardous
situation which, if not avoided, could result in
death or serious injury.
nCAUTION
CAUTION Indicates a potentially hazardous
situation which, if not avoided, may result in
minor or moderate injury.
CAUTION
CAUTION used without the safety alert symbol
indicates a potentially hazardous situation which,
if not avoided, may result in property damage.
DEFINITIONS
This appliance must be installed by qualified and licensed personnel in accordance with
local codes, or in the absence of local codes, by the national fuel gas code, ANSI Z223.1-
2002. This appliance is for indoor installations only. Clearance to combusitble materials: 0”
top, bottom, sides and back. Front must have room for service, 24” recommended. (A
combustible door or removable panel is acceptable front clearance.) This appliance has
been approved for closet installation. Do not install this appliance directly on carpeting. For
installation on combustible flooring directly. Category IV vent systems only.

GAS-FIRED BOILER Boiler Manual
5
PART 1: PRODUCT AND SAFETY INFORMATION (CONT’D)
BEFORE INSTALLING
WHEN SERVICING BOILER
• To avoid electric shock, disconnect electrical
supply before performing maintenance.
• To avoid severe burns, allow boiler to cool
before performing maintenance.
BOILER OPERATION
• Do not block flow of combustion or
ventilation air to boiler.
• Should overheating occur or gas supply fail to
shut off, do not turn off or disconnect electrical
supply to circulator. Instead, shut off the gas
supply at a location external to the appliance.
• Do not use this boiler if any part has been
under water. Immediately call a qualified
service technician to inspect the boiler and to
replace any part of the control system and
any gas control that has been under water.
BOILER WATER
• If you have an old system with cast iron
radiators, thoroughly flush the system (without
boiler connected) to remove sediment. The
high-efficiency heat exchanger can be damaged
by build-up or corrosion due to sediment. HTP
recommends a suction strainer in this type of
system.
• Do not use petroleum-based cleaning or sealing
compounds in boiler system. Gaskets and seals
in the system may be damaged. This can result
in substantial property damage.
• Do not use “homemade cures” or “boiler patent
medicines.” Substantial property damage,
damage to boiler, and/or serious personal injury
nWARNING
Installer — Read all instructions in this manual,
and Mod Con Venting section, before installing.
Perform steps in the order given.
User — This manual is for use only by a
qualified heating installer/service technician.
Refer to User’s Information Manual for your
reference.
User — Have this boiler serviced/inspected by
a qualified service technician annually.
Failure to comply with the above could result in
severe personal injury, death or substantial
property damage.
nWARNING
Failure to adhere to the guidelines on this page
can result in severe personal injury, death or
substantial property damage.
nWARNING
WHAT TO DO IF YOU SMELL GAS
• Do not try to light any appliance.
• Do not touch any electric switch; do not use
any phone in your building.
• Immediately call your gas supplier from a
neighbor's phone. Follow the gas suppliers'
instructions.
• If you cannot reach your gas supplier, call the
fire department.
CAUTION
Due to the low water content of the boiler, mis-
sizing of the boiler with regard to the heating
system load will result in excessive boiler
cycling and accelerated component failure. Heat
Transfer Products DOES NOT warrant failures
caused by mis-sized boiler applications. DO
NOT oversize the boiler to the system. Modular
boiler installations greatly reduce the likelihood
of boiler oversizing.

GAS-FIRED BOILER Boiler Manual
6
PART 2: BEFORE YOU START
A. WHAT’S IN THE BOX
Also included with the Mod Con are:
• Pressure and Temperature Gauge
• Outdoor Sensor
• Installation Manual
• Warranty
• CSD-1 Form
• H-3 Data Sheet
B. HOW BOILER OPERATES
Mod/Con Condensing Technology is an intelli-
gent system that delivers highly efficient
hydronic heating, while maximizing efficiency
by measuring the data parameters of your heat-
ing system. Outlined below are the features of
the system and how they operate:
1. Stainless Steel Heat Exchanger – The highly
efficient Mod/Con Stainless Steel Heat
exchanger is designed to use the cold return
water from the system and extract the last bit
of heat before it is exhausted.
2. Modulating Combustion System – The
combustion system will modulate the output
of the burner during operation to match the
system demand and achieve the control set
point while in operation. The set point can
change by internal or external signals which
enhance the overall performance of the
system.
3. Control – The integrated control system
monitors the system and regulates the fan
speed to control the boilers output. This
allows the boiler to only deliver the amount
of heated energy required and nothing more.
This control can be set up to monitor outdoor
temperature through an outdoor sensor to
regulate the set point of the boiler. The
system can be further enhanced by
connecting up to an indirect water heater to
provide domestic hot water.
The control can regulate the output of
multiple boilers through its cascade system
function. The cascade system is capable of
connecting up to eight boilers together in
such a way that they function as one boiler
system. This allows for greater turn down
ratios and provides systematic control of the
multiple boilers in an installation to minimize
downtime and maximize efficiency.
The cascade system works by establishing
one boiler as the master and the other
connected boilers as followers. The master
boiler will have a cascade system sensor and
a cascade pump connected to it in addition to
its own boiler pump. The follower boilers will
PART 1: PRODUCT AND SAFETY INFORMATION (CONT’D)
CAUTION
Consider piping and installation when
determining boiler location.
nCAUTION
NEVER use automotive or standard glycol
antifreeze, ethylene glycol made for hydronic
systems. Use only inhibited propylene glycol
solutions, which are specifically formulated for
hydronic systems. Ethylene glycol is toxic and
can attack gaskets and seals used in hydronic
systems.
may result.
• Continual fresh make-up water will reduce boiler
life. Mineral buildup in the heat exchanger
reduces heat transfer, overheats the stainless
steel heat exchanger, and causes failure.
Addition of oxygen carried in by make-up water
can cause internal corrosion in system
components. Leaks in boiler or piping must be
repaired at once to prevent make-up water.
FREEZE PROTECTION FLUIDS

GAS-FIRED BOILER Boiler Manual
7
PART 2: BEFORE YOU START (CONT’D)
have their own individual pump connected to
each follower boiler.
4. System Display and Operation Led light
Indicators – The display allows the user to
change the system parameters and monitor
the system outputs. Led light indicators
monitor operation through illumination of
Indirect Pump – Boiler Pump – System Pump
– Flame On – System Fault.
5. Gas Valve – The gas valve senses suction
from the blower allowing gas to flow only if
the gas valve is powered and combustion air
is flowing.
6. Swirl Plate or Integrated Venturi – Controls
the air and gas flow into the burner.
7. Burner – Constructed of high grade stainless
steel, the burner uses premixed air gas and
provides a wide range of firing rates.
8. Spark Ignition – The burner is ignited by
applying a high voltage through the system
spark electrode. This causes the spark from
the electrode to ignite the mixed gas off of
the burner.
9. Supply Water Temperature Sensor – This
sensor monitors the boiler outlet water
temperature (System Supply). The control
adjusts the boiler firing rate so the supply
temperature will match the boiler set point.
10. Return Water Temperature Sensor – This
sensor monitors the boiler return water
temperature (System Return). The control
adjusts the boiler firing depending on how
close the return water temperature is to the
supply water temperature.
11. Temperature and Pressure Gauge – Allows
the user to monitor the system temperature
and pressure.
12. Electrical field connections with terminal
strips – The electrical cover allows easy
access to the line voltage and low voltage
terminals strips which are clearly marked to
facilitate wiring of the boiler.
13. Condensation Collection System – This boiler
is a high efficiency appliance, therefore the
boiler will produce condensate. The collection
system has a float switch to monitor the
condensation level to prevent condensation
from backing up into the combustion system.
Inside the collection system there is a built in
trap to seal the combustion system to the
connected drain. This condensate should be
neutralized to avoid damage to the drainage
system or piping.
14. Outdoor Sensor – The outdoor sensor will
monitor the outdoor temperature and adjust
the unit’s set point to provide greater
efficiency.
C. OPTIONAL EQUIPMENT
Below is the list of optional equipment available
for Mod Con Boiler.
• System Sensor (Part # 7250P-324)
• Indirect Sensor (Part # 7250P-325)
• 4” Stainless Steel Outside Termination Vent
Kit (V3000)
• 6” Stainless Steel Outside Termination Vent
Kit (V4000)
• High and Low Gas Pressure Switch Kit with
Manual Reset (Part # 7350P-600)
• U.L. 353 Compliant Low Water Cut-Off
Interface Kit with Manual Reset (Part # 7350P-
601)
• Alarm System (Part # 7350P-602) (to monitor
any failure)
• Stacking Kit (Part # 7350P-603)
• PC Connection Kit (Part # 7350P-320)
• Boiler Caster Kit (Part # 7350P-404)
• Mod Con Condensate Neutralizer (Part #
7350P-611)
These additional options may be purchased
through your HTP Distributor.
PART 3: PREPARE BOILER LOCATION
A. BOILER LOCATION SHOULD BE LEVEL
Before considering the Boiler location, there are
many factors that have to be addressed that are
covered in detail in this installation manual.
Please read the entire manual as it could save

8
GAS-FIRED BOILER Boiler Manual
nCAUTION
When preparing the boiler location, make sure the area where you are placing the boiler is level. In order
for the condensate properly to flow out of the collection system, the boiler must be level to assure proper
flow direction. The Mod Con Boiler comes equipped with leveling feet. Should you find the floor beneath
the boiler is uneven, with a wrench, adjust the leveling feet.
INCORRECT CORRECT
INCORRECT CORRECT
PART 3: PREPARE BOILER LOCATION (CONT’D)
time and money. Piping, Venting, Condensation
Removal are just a few issues that need to be addressed prior to the installation of the boiler.

GAS-FIRED BOILER Boiler Manual
9
Figure 2-1
DIMENSIONS
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• Incorrectly-sized expansion tank.
• Lack of freeze protection in boiler water
causing system and boiler to freeze and leak.
• Excessive glycol which will affect the
boiler system operation.
• Clean and flush system when re-installing
a boiler.
D. CLEARANCES FOR SERVICE ACCESS
1. See Figure 3-1 for recommended service
clearances. If you do not provide minimum
clearances shown, it might not be possible to
service the boiler without removing it from
the space.
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nWARNING
The space must be provided with combus-
tion/ventilation air openings correctly sized for
all other appliances located in the same space as
the Mod Con Boiler. The boiler cover must be se-
curely fastened to the boiler to prevent the boil-
er from drawing air from inside the boiler room.
This is particularly important if the boiler is lo-
cated in the same room as other appliances.
Failure to comply with the above warnings could
result in severe personal injury, death or sub-
stantial property damage.
Figure 3-1 LP-205-M Rev. 5/27/08
SERVICE CLEARANCES
PART 3: PREPARE BOILER LOCATION (CONTINUED)
B. INSTALLATIONS MUST COMPLY WITH:
• Local, state, provincial, and national codes,
laws, regulations and ordinances.
• National Fuel Gas Code, ANSI Z223.1 – latest
edition.
• Standard for Controls and Safety Devices for
Automatically Fired Boilers, ANSI/ASME
CSD-1, when required.
• National Electrical Code.
• For Canada only: B149.1 or B149.2
Installation Code, CSA C22.1 Canadian
Electrical Code Part 1 and any local codes.
C. BEFORE LOCATING THE BOILER
1. Check for nearby connections to:
• System water piping
• Venting connections
• Gas supply piping
• Electrical power
• Condensate drain
2. Check area around boiler. Remove any
combustible materials, gasoline and other
flammable liquids.
3. The Mod Con Gas Control System
components must be protected from dripping
water during operation or service.
4. If the Mod Con Boiler is to replace an existing
boiler, check for and correct any existing
system problems such as:
• System leaks.
NOTICE
The Mod Con Boiler gas manifold and controls
met safe lighting and other performance criteria
when the boiler underwent tests specified in
ANSI Z21.13 — latest edition.
nWARNING
Failure to keep boiler area clear and free of
combustible materials, gasoline and other
flammable liquids and vapors can result in
severe personal injury, death or substantial
property damage.
GAS-FIRED BOILER Boiler Manual
10

GAS-FIRED BOILER Boiler Manual
11
E. RESIDENTIAL GARAGE INSTALLATION
Precautions
Take the following special precautions when
installing the boiler in a residential garage. If the
boiler is located in a residential garage, per ANSI
Z223.1, paragraph 5.1.9:
• Mount the boiler with a minimum of 18
inches above the floor of the garage to the
bottom of the boiler to ensure the burner and
ignition devices will be no less than 18 inches
above the floor.
• Locate or protect the boiler so it cannot be
damaged by a moving vehicle.
F. EXHAUST VENT AND INTAKE AIR VENT
The Mod Con Boiler requires a special vent sys-
tem, designed for pressurized venting. Mod Con
Boilers are rated ANSI Z21.13 Category IV (pres-
surized vent, likely to form condensate in the
vent).
You must also install air intake piping from out-
doors to the boiler flue adaptor. The resultant
installation is categorized as direct vent (sealed
combustion). Note: To prevent combustion
air contamination see Table 3-2 in this
section when considering exhaust vent
and intake air vent termination.
Intake and exhaust must terminate near each
other and may be vented vertically through the
roof or out a side wall. The intake and exhuast
venting methods are detailed in the Venting
Section. Do not attempt to install the Mod Con
Boiler using any other means. Be sure to locate
the boiler such that the air intake and exhaust
vent piping can be routed through the building
and properly terminated. The air intake and
exhaust vent piping lengths, routing and termi-
nation method must all comply with the methods
and limits given in the venting section.
PART 3: PREPARE BOILER LOCATION (CONTINUED)
G. PREVENT COMBUSTION AIR
CONTAMINATION
Install intake air piping for the Mod Con Boiler as
described in the Venting section. Do not termi-
nate exhaust in locations that can allow contam-
ination of intake air.
nWARNING
You must pipe outside air to the boiler air
intake. Ensure that the intake air will not
contain any of the contaminants below.
Contaminated air will damage the boiler,
resulting in possible severe personal injury,
death or substantial property damage. For
example, do not pipe intake air vent near a
swimming pool. Also avoid areas subject to
exhaust fumes from laundry facilities. These
areas will always contain contaminants.
Products to avoid
Spray cans containing fluorocarbons
Permanent wave solutions
Chlorinated waxes/cleaners
Chlorine-based swimming pool chemicals
Calcium chloride used for thawing
Sodium chloride used for water softening
Refrigerant leaks
Paint or varnish removers
Hydrochloric acid/muriatic acid
Cements and glues
Antistatic fabric softeners used in clothes dryers
Chlorine-type bleaches, detergents, and cleaning
solvents found in household laundry rooms
Adhesives used to fasten building products and
other similar products
Areas likely to have contaminants
Dry cleaning/laundry areas and establishments
Swimming pools
Metal fabrication plants
Beauty shops
Refrigeration repair shops
Photo processing plants
Auto body shops
Plastic manufacturing plants
Furniture refinishing areas and establishments
New building construction
Remodeling areas
Garages and workshops
Table 3-2: Corrosive contaminants and sources
nWARNING
Vents must be properly supported. The Mod
Con’s Intake and Exhaust Connections are not
designed to carry heavy weight. Vent support
brackets must be within 1 foot of the boiler and
the balance at 4 foot intervals. The Mod Con
venting must be readily accessible for visual
inspection for the first three feet from the boiler.

H. WHEN REMOVING A BOILER FROM AN
EXISTING COMMON VENT SYSTEM
At the time of removal of an existing boiler, the
following steps shall be followed with each
appliance remaining connected to the common
venting system placed in operation, while the
other appliances remaining connected to the
common venting system are not in operation.
a. Seal any unused openings in the common
venting system.
b. Visually inspect the venting system for
proper size and horizontal pitch and
determine that there is no blockage or
restriction, leakage, corrosion or other
deficiencies which could cause an unsafe
condition.
c. Insofar as is practical, close all building doors
and windows and all doors between the
space in which the appliances remaining
connected to the common venting system
are located and other spaces of the building.
Turn on clothes dryers and any appliance not
connected to the common venting system.
Turn on any exhaust fans, such as range
hoods and bathroom exhausts, so they will
operate at maximum speed. Do not operate
a summer exhaust fan. Close fireplace
dampers.
d. Place in operation the appliance being
inspected. Follow the lighting instructions.
Adjust thermostat so appliance will operate
continuously.
e. Test for spillage at draft hood opening after 5
minutes of main burner operation. Use the
flame of a match or candle, or smoke from a
cigarette, cigar, or pipe.
f. After it has been determined that each
appliance remaining connected to the
common venting system properly vents
when tested as outlined herein, return doors,
windows, exhaust fans, fireplace dampers
and any other gas-burning appliance to their
previous conditions of use.
g. Any improper operation of common venting
system should be corrected so the
installation conforms with the National Fuel
Gas Code, ANSI Z223.1 — latest edition.
Correct by resizing to approach the minimum
size as determined using the appropriate
tables in Table 13 of NFPA54 ANSI Z223.1
2006 of that code. Canadian installations
must comply with B149.1 or B149.2
Installation Code.
PART 3: PREPARE BOILER LOCATION (CONTINUED)
PART 4: PREPARE BOILER
nWARNING
Failure to follow all instructions can result in flue
gas spillage and carbon monoxide emissions,
causing severe personal injury or death.
Remove all sides of the Mod Con shipping crate
in order to allow the boiler to be lifted into its
installation location. You must pick the boiler up
by the lift rings to avoid damage to the boiler
CAUTION
Cold weather handling — If boiler has been
stored in a very cold location (below 0°F) before
installation, handle with care until the plastic
components come to room temperature.
GAS-FIRED BOILER Boiler Manual
12
nDANGER
Do not install the Mod Con Boiler into a common
vent with any other appliance. This will cause
flue gas spillage or appliance malfunction,
resulting in possible severe personal injury,
death or substantial property damage.
nWARNING
Uncrating Boiler – Any Claims for damage or
shortage in shipment must be filed immediately
against the transportation company by the
consignee.

PART 4: PREPARE BOILER (CONTINUED)
GAS-FIRED BOILER Boiler Manual
13
A. RELIEF VALVE
Connect discharge piping to a safe disposal location, follow the guidelines in the WARNING below.
PART 5: BOILER PIPING
nWARNING
To avoid water damage or scalding due to relief valve operation:
• Discharge line must be connected to relief valve outlet and run to a safe place of disposal. Terminate
the discharge line in a manner that will prevent possibility of severe burns or property damage should
the valve discharge.
• Discharge line must be as short as possible and be the same size as the valve discharge connection
throughout its entire length.
• Discharge line must pitch downward from the valve and terminate at least 6” above the floor drain
where any discharge will be clearly visible.
• The discharge line shall terminate plain, not threaded, with a material serviceable for temperatures of
375 °F or greater.
• Do not pipe the discharge to any place where freezing could occur.
• No shutoff valve shall be installed between the relief valve and boiler, or in the discharge line. Do not
plug or place any obstruction in the discharge line.
• Test the operation of the valve after filling and pressurizing system by lifting the lever. Make sure the
valve discharges freely. If the valve fails to operate correctly, replace it with a new relief valve.
• Failure to comply with the above guidelines could result in failure of the relief valve to operate,
resulting in possibility of severe personal injury, death or substantial property damage.
enclosure. You can use either a solid
¾” in diameter black iron pipe or lift-
ing straps to lift the boiler off of its
shipping crate. You must have at least
two individuals to handle the boiler
properly to avoid damage as care
should be taken as the Mod Con is
very heavy. The Mod Con is also
equipped with leveling feet that can
be used to level the boiler properly if
the surface location is not level. If sur-
face flooring is rough, care should be
taken when sliding boiler into posi-
tion, you could catch the leveling feet
and damage the boiler if it is slid to its
location.
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PART 5: BOILER PIPING (CONTINUED)
B. GENERAL PIPING INFORMATION
C. BACKFLOW PREVENTER
Use a backflow preventer specifically designed
for hydronic boiler installations. This valve
should be installed on the cold water fill supply
line per local codes. (See Boiler Piping Details)
D. SYSTEM WATER PIPING METHODS
Expansion tank and make-up water
1. Ensure that the expansion tank size will
handle boiler and system water volume and
temperature. Allow for boiler and its piping:
2. The expansion tank must be located as
shown in Boiler Piping Part 5 or following
recognized design methods. See tank
manufacturer’s instructions for details.
3. Connect the expansion tank to the air
separator only if the separator is on the
suction side of the circulator. Always install
the system fill connection at the same point
as the expansion tank connection to the
system.
4. Most chilled water systems are piped using a
closed type expansion tank.
Diaphragm (or bladder) expansion tank
1. Always install an automatic air vent on top of
the air separator to remove residual air from
the system.
E. CIRCULATORS
Sizing space heat system piping
1. See Piping Details in this manual Part 5. In all
diagrams, the space heating system is
isolated from the boiler loop by the
primary/secondary connection.
2. Size the piping and components in the space
heating system using recognized design
methods.
F. HYDRONIC PIPING WITH CIRCULATORS,
ZONE VALVES AND MULTIPLE BOILERS
The Mod Con Boiler is designed to function in a
closed loop Hydronic System. We have also in-
cluded a Temperature and Pressure gauge that al-
nCAUTION
DO NOT install automatic air vents on closed-
type expansion tank systems. Air must remain
in the system and return to the tank to provide
its air cushion. An automatic air vent would
cause air to leave system, resulting in water-
logging the expansion tank.
nCAUTION
DO NOT use the boiler circulator in any location
other than the ones shown in this manual. The
boiler circulator is selected to ensure adequate
flow through the Mod Con Boiler. Failure to
comply could result in unreliable performance
and nuisance shut downs from insufficient flow.
CAUTION
Undersized expansion tanks cause system
water to be lost from relief valve and makeup
water to be added through a fill valve. Eventual
boiler failure can result due to excessive make-
up water addition. This type of failure is NOT
covered by warranty.
GAS-FIRED BOILER Boiler Manual
14
NOTICE
The Mod Con Boiler control module uses
temperature sensors to provide both high limit
protection and modulating temperature control.
The control module also provides low water
protection by sensing the water level in the heat
exchanger. Some codes/jurisdictions may
require additional external controls.
CAUTION
All piping methods shown in this manual use
primary/secondary connection to the boiler loop.
This is to avoid the possibility of inadequate flow
through the boiler. For other piping methods,
consult your local Heat Transfer Products
representative or refer to separate Mod Con
Boiler piping details in this manual (Part 5).
Mod Con 300 2.9 Gallons
Mod Con 500 4.2 Gallons
Mod Con 850 5.8 Gallons

PART 5: BOILER PIPING (CONTINUED)
GAS-FIRED BOILER Boiler Manual
15
lows the user to monitor the system pressure and
outlet temperature from the Mod Con Boiler. It is
important to note that the Mod Con Boiler has a
minimal amount of pressure drop and must be cal-
culated when sizing the circulators. Each Mod Con
Boiler installation must have an Air Elimination de-
vice that will remove air from the system. Install the
Mod Con Boiler so the gas ignition system com-
ponents are protected from water (dripping, spray-
ing, etc.) allowing clearance for basic service of
boiler circulator, valves and other components.
Observe minimum 1” clearance around all un-in-
sulated hot water pipes when openings around
pipes are not protected by non-combustible ma-
terials. On a Mod Con Boiler installed above radia-
tion level, some states and local codes require a
low water cut off device which is standard on the
Mod Con boiler. Check with local codes for addi-
tional requirements. If the Mod Con Boiler supplies
hot water to heating coils in air handler units, flow
control valves or other devices must be installed to
prevent gravity circulation of boiler water in the
coils during the cooling cycle. Chilled Water
Medium must be piped in parallel with the boiler.
Freeze Protection for new or existing systems must
use glycol that is specifically formulated for this
purpose. It will include inhibitors that will prevent
the glycol from attacking the metallic system com-
ponents. Make certain that the system fluid is
checked for the correct glycol concentration and in-
hibitor level. The system should be tested at least
once a year and as recommend by the producer of
the glycol solution. Allowance should be made for
the expansion of the glycol solution in the system
piping. Example 50% by volume gycol solution ex-
pands 4.8% in volume for the temperature increase
from 32 F to 180 F, while water expands 3% with
the same temperature rise.

Single Mod Con Boiler Space Heating with Indirect Priority
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LP-205-L Rev. 5/14/08
PART 5: BOILER PIPING (CONTINUED)
GAS-FIRED BOILER Boiler Manual
16
G. BOILER PIPING DETAILS
NOTES:
1. This drawing is meant to show system piping concept only.
2. An Anti-Scald mixing valve is recommended if the DHW temperature is set above the factory setting
of 119°F.
3. Install a minimum of 12 diameters of straight pipe upstream of all circulators.
4. Piping shown is Primary/Secondary
5. System Flow (Secondary Loop) must be greater than the boiler’s primary loop flow.

Cascade Multiple Mod Con Boilers with
Indirect Priority on One Boiler
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LP-205-J Rev. 5/14/08
PART 5: BOILER PIPING (CONTINUED)
NOTES:
1. This drawing is meant to show system piping concept only.
2. An Anti-Scald mixing valve is recommended if the DHW temperature is set above the factory setting
of 119°F.
3. Install a minimum of 12 diameters of straight pipe upstream of all circulators.
4. Piping shown is Primary/Secondary
5. Reference Figure 5-2 to determine manifold pipe sizing.
6. System Flow (Secondary Loop) must be greater than the boiler’s primary loop flow.
GAS-FIRED BOILER Boiler Manual
17

Single Mod Con Boiler
Space Heating
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LP-205-R Rev. 5/14/08
PART 5: BOILER PIPING (CONTINUED)
GAS-FIRED BOILER Boiler Manual
18
NOTES:
1. This drawing is meant to show system piping concept only.
2. Install a minimum of 12 diameters of straight pipe upstream of all circulators.
3. Piping shown is Primary/Secondary
6. System Flow (Secondary Loop) must be greater than the boiler’s primary loop flow.

Cascade Mod Con Boilers
Space Heating Only
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LP-205-Q Rev. 5/14/08
PART 5: BOILER PIPING (CONTINUED)
NOTES:
1. This drawing is meant to show system piping concept only.
2. An Anti-Scald mixing valve is recommended if the DHW temperature is set above the factory setting
of 119°F.
3. Install a minimum of 12 diameters of straight pipe upstream of all circulators.
6. System Flow (Secondary Loop) must be greater than the boiler’s primary loop flow.
GAS-FIRED BOILER Boiler Manual
19