HTP 500 LP Installation manual

120 Braley Rd. P.O. Box 429 East Freetown, MA 02717-0429 www.htproducts.com
LP- 446 REV. 9.3.14
Mod Con VWH
INSTALLATION
START-UP
MAINTENANCE
PARTS
VWH Models
500 / 850
LP / HL / LPHL
THIS MANUAL IS FOR USE WITH MOD CON BOILERS MANUFACTURED AFTER
DECEMBER 1, 2012
Heat Exchanger Bears the ASME “H” Stamp
Improper installation, adjustment, alteration, service, or maintenance could void product warranty and cause property damage, personal
injury, or death.
NOTICE: HTP reserves the right to make product changes or updates without notice and will not be held liable for typographical errors
in literature.
The surfaces of these products contacted by consumable water contain less than 0.25% lead by weight, as required by the Safe
Drinking Water Act, Section 1417.
NOTE TO CONSUMER: PLEASE KEEP ALL INSTRUCTIONS FOR FUTURE REFERENCE.
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 substantial property damage, severe personal injury, or death.

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LP- 446 REV. 9.3.14
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 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 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 provided by a qualified installer,
service agency, or the gas supplier.

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LP- 446 REV. 9.3.14
The following defined terms are used throughout this manual to bring attention to the presence of hazards of various risk
levels, or to important product information.
DANGER indicates an imminently hazardous situation which, if not avoided, will result in death or serious injury.
WARNING indicates a potentially hazardous situation which, if not avoided, could result in death or serious injury.
CAUTION indicates a potentially hazardous situation which, if not avoided, may result in minor or moderate injury.
CAUTION used without the safety alert symbol indicates a potentially hazardous situation which, if not avoided, may result in property
damage.
FOREWORD
This manual is intended to be used in conjunction with other literature provided with the appliance. This includes all related control
information. It is important that this manual, all other documents included with this system, and additional publications including the
National Fuel Gas Code, ANSI Z223.1-2002, be reviewed in their entirety before beginning any work.
Installation should be made in accordance with the regulations of the Authority Having Jurisdiction, local code authorities, and utility
companies which pertain to this type of water heating equipment.
Authority Having Jurisdiction (AHJ) –The Authority Having Jurisdiction may be a federal, state, local government, or individual such
as a fire chief, fire marshal, chief of a fire prevention bureau, labor department or health department, building official or electrical
inspector, or others having statutory authority. In some circumstances, the property owner or his/her agent assumes the role, and at
government installations, the commanding officer or departmental official may be the AHJ.
NOTE: HTP, Inc. reserves the right to modify product technical specifications and components without prior notice.
FOR THE INSTALLER
This appliance must be installed by qualified and licensed personnel. The installer should be guided by the instructions furnished with
the boiler, and with local codes and utility company requirements. In the absence of local codes, preference should be given to the
National Fuel Gas Code, ANSI Z223.1-2002.
INSTALLATIONS MUST COMPLY WITH:
Authority Having Jurisdiction, local, state, provincial, and national codes, laws, regulations and ordinances.
The latest version of the National Fuel Gas Code, ANSI Z223.1, from American Gas Association Laboratories, 8501 East Pleasant
Valley Road, Cleveland, OH 44131.
In Canada –CGA No. B149 (latest version), from Canadian Gas Association Laboratories, 55 Scarsdale Road, Don Mills, Ontario,
Canada M3B 2R3. Also, Canadian Electrical Code C 22.1, from Canadian Standards Association, 5060 Spectrum Way, Suite 100,
Mississauga, Ontario, Canada L4W 5N6.
Code for the installation of Heat Producing Appliances (latest version), from American Insurance Association, 85 John Street, New
York, NY 11038.
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 substantial property damage, severe personal injury, or death.

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LP- 446 REV. 9.3.14
The latest version of the National Electrical Code, NFPA No. 70.
NOTE: The gas manifold and controls met safe lighting and other performance criteria when the boiler underwent tests specified in
ANSI Z21.13 –latest edition.
NOTICE
The CSD-1 ASME Code, Section CW-400 requires that hot water heating and supply boilers have a) a UL 353 temperature control
device, b) at least one (1) temperature-actuated control to shut off the fuel supply when system water reaches a preset operating
temperature, c) a high temperature limit control that prevents the water temperature from exceeding the maximum allowable
temperature by causing a safety shutdown and lockout, and d) its own sensing element and operating switch.
The temperature control system integrated into the 926 control provided with this heating appliance complies with the requirements of
CSD-1 Section CW-400 as a temperature operation control. The control monitors the temperature difference between the inlet and the
outlet sensor, which is affected by boiler water flow. If this temperature difference exceeds 55°F (typically because of low water flow or
very low heat load), the control will reduce the maximum fan speed. If the temperature difference exceeds 60°F, the control will
effectively sense there is little or no water flow or heat load and shut the boiler down. The controller will restart automatically once the
temperature difference has dropped below 55°F and the minimum off time (anti-cycle time) has expired. In addition, if the control
senses that the outlet water temperature has reached 210°F, the boiler is put into a hard lockout and requires manual reset to restart.
TABLE OF CONTENTS
PART 1 –GENERAL SAFETY INFORMATION..........................................................................................................................6
A. PRECAUTIONS..........................................................................................................................................................................6
B. IMPROPER COMBUSTION........................................................................................................................................................7
C. GAS............................................................................................................................................................................................7
D. WHEN SERVICING THE BOILER..............................................................................................................................................7
E. BOILER WATER.........................................................................................................................................................................7
PART 2 –BEFORE YOU START................................................................................................................................................7
A. WHAT’S IN THE BOX .................................................................................................................................................................8
B. HOW BOILER OPERATES.........................................................................................................................................................9
C. OPTIONAL EQUIPMENT .........................................................................................................................................................10
PART 3 –PREPARE BOILER LOCATION ...............................................................................................................................10
A. BEFORE LOCATING THE BOILER..........................................................................................................................................10
B. LEVELING AND DIMENSIONS ................................................................................................................................................11
C. CLEARANCES FOR SERVICE ACCESS.................................................................................................................................13
D. RESIDENTIAL GARAGE INSTALLATION................................................................................................................................13
E. EXHAUST VENT AND INTAKE PIPE.......................................................................................................................................13
F. PREVENT COMBUSTION AIR CONTAMINATION..................................................................................................................13
G. REMOVING A BOILER FROM A COMMON VENT SYSTEM..................................................................................................14
H. UNCRATING AND MOVING BOILER ......................................................................................................................................15
PART 4 –BOILER PIPING........................................................................................................................................................15
A. GENERAL PIPING INFORMATION..........................................................................................................................................15
B. RELIEF VALVE.........................................................................................................................................................................15
C. SYSTEM WATER PIPING METHODS.....................................................................................................................................16
D. CIRCULATOR PUMPS.............................................................................................................................................................16
E. SCALDING................................................................................................................................................................................17
F. HIGH VELOCITY CIRCULATOR PUMP...................................................................................................................................17
G. WATER CHEMISTRY...............................................................................................................................................................19

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LP- 446 REV. 9.3.14
H. PIPING DIAGRAMS..................................................................................................................................................................21
PART 5 –VENTING, COMBUSTION AIR AND CONDENSATE REMOVAL............................................................................27
A. GENERAL.................................................................................................................................................................................27
B. APPROVED MATERIALS FOR EXHAUST VENT AND INTAKE PIPE ....................................................................................28
C. REQUIREMENTS FOR INSTALLATION IN CANADA..............................................................................................................29
D. EXHAUST VENT AND INTAKE PIPE LOCATION....................................................................................................................30
E. EXHAUST VENT AND INTAKE PIPE SIZING..........................................................................................................................33
F. LONGER VENT RUNS .............................................................................................................................................................33
G. EXHAUST VENT AND INTAKE PIPE INSTALLATION ............................................................................................................33
H. BOILER REMOVAL FROM A COMMON VENT SYSTEM .......................................................................................................34
I. SIDEWALL VENTING DIAGRAMS ............................................................................................................................................35
J. VERTICAL VENTING DIAGRAMS............................................................................................................................................37
K. ROOM AIR, INDOOR COMBUSTION, AND VENTILATION AIR INSTALLATION REQUIREMENTS .....................................40
PART 6 –GAS PIPING..............................................................................................................................................................41
A. GAS CONNECTION .................................................................................................................................................................41
B. GAS PIPING .............................................................................................................................................................................42
C. GAS TABLE..............................................................................................................................................................................42
D. CHECK INLET GAS PRESSURE.............................................................................................................................................43
E. GAS VALVE..............................................................................................................................................................................44
PART 7 –FIELD WIRING..........................................................................................................................................................46
A. INSTALLATION MUST COMPLY WITH:..................................................................................................................................46
B. FIELD WIRING TERMINATIONS..............................................................................................................................................46
C. FIELD WIRING CONSIDERATIONS........................................................................................................................................46
D. LINE VOLTAGE WIRING..........................................................................................................................................................47
E. ALARM CONNECTIONS ..........................................................................................................................................................47
F. LOW VOLTAGE CONNECTIONS FOR STANDARD BOILER .................................................................................................48
G. TANK SENSOR OR MECHANICAL CONTROL.......................................................................................................................48
H. SYSTEM / PIPE SENSOR........................................................................................................................................................48
I. OPTIONAL HIGH GAS PRESSURE SWITCH...........................................................................................................................48
J. OPTIONAL LOW GAS PRESSURE SWITCH...........................................................................................................................48
K. FLOW SWITCH.........................................................................................................................................................................48
L. WIRING OF THE CASCADE SYSTEM COMMUNICATION BUS.............................................................................................48
M. VWH CASCADE MASTER PUMP AND SENSOR WIRING.....................................................................................................49
N. VWH CASCADE FOLLOWER PUMP AND SENSOR WIRING................................................................................................51
PART 8 –START-UP PREPARATION......................................................................................................................................53
A. CHECK / CONTROL WATER CHEMISTRY.............................................................................................................................53
B. CHECK FOR GAS LEAKS........................................................................................................................................................53
C. CONDENSATE REMOVAL ......................................................................................................................................................53
D. FINAL CHECKS BEFORE STARTING HEATER......................................................................................................................54
E. SETTING UP A SINGLE HEATER............................................................................................................................................54
F. SETTING UP A CASCADED SYSTEM.....................................................................................................................................54

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LP- 446 REV. 9.3.14
G. LOCKOUT CONDITION ...........................................................................................................................................................55
H. CASCADE SYSTEM PROGRAMMING....................................................................................................................................55
PART 9 –START-UP PROCEDURE.........................................................................................................................................56
A. CONTROL OVERVIEW ............................................................................................................................................................56
B. NAVIGATION OF THE DISPLAY..............................................................................................................................................56
C. OPERATING INSTRUCTIONS.................................................................................................................................................57
D. PROGRAMMING HEATER SETTINGS....................................................................................................................................57
E. PROGRAMMING THE SYSTEM SETTING..............................................................................................................................58
F. SYSTEM SETTING PROGRAM NAVIGATION.........................................................................................................................58
G. RESETTING THE MAINTENANCE SCHEDULE......................................................................................................................60
PART 10 –START-UP PROCEDURES FOR THE INSTALLER...............................................................................................61
A. HEATER CONTROL STATUS MENU ......................................................................................................................................61
B. CASCADE MENU.....................................................................................................................................................................62
C. HEATER TEST MODE .............................................................................................................................................................63
PART 11 –TROUBLESHOOTING ............................................................................................................................................63
A. HEATER ERROR CODE..........................................................................................................................................................63
B. HEATER ERROR......................................................................................................................................................................63
C. HEATER FAULT.......................................................................................................................................................................63
D. USER INTERFACE DISPLAY ..................................................................................................................................................64
PART 12 –MAINTENANCE ......................................................................................................................................................69
A. MAINTENANCE PROCEDURES..............................................................................................................................................69
B. COMBUSTION CHAMBER COIL CLEANING INSTRUCTIONS FOR HEATER ......................................................................70
C. CLEANING WATER SIDE OF HEAT EXCHANGER................................................................................................................70
BOILER START-UP REPORT...................................................................................................................................................75
MAINTENANCE REPORT.........................................................................................................................................................75
MAINTENANCE NOTES..................................................................................................................................................................79
HTP CUSTOMER INSTALLATION RECORD FORM......................................................................................................................80
PART 1 –GENERAL SAFETY INFORMATION
A. PRECAUTIONS
This appliance is for indoor installations only. Clearance to combustible 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. This appliance may be installed on combustible
flooring. For use with Category IV vent systems only.
INSTALLER –Read all instructions in this manual 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. Have this boiler serviced/inspected by a qualified service technician annually.
FAILURE TO ADHERE TO THE GUIDELINES ON THIS PAGE AND HAVE THIS BOILER SERVICED/INSPECTED ANNUALLY
CAN RESULT IN SUBSTANTIAL PROPERTY DAMAGE, SEVERE PERSONAL INJURY, OR DEATH.

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LP- 446 REV. 9.3.14
DO NOT USE THIS APPLIANCE IF ANY PART HAS BEEN SUBMERGED IN WATER. Immediately call a qualified service technician.
The appliance MUST BE replaced if it has been submerged. Attempting to operate an appliance that has been submerged could create
numerous harmful conditions, such as a potential gas leakage causing a fire and/or explosion, or the release of mold, bacteria, or other
harmful particulates into the air. Operating a previously submerged appliance could result in property damage, severe personal injury,
or death.
NOTE: Appliance damage due to flood or submersion is considered an Act of God, and IS NOT covered under product warranty.
NOTE: If the boiler is exposed to the following, do not operate until all corrective steps have been made by a qualified serviceman:
FIRE
DAMAGE
WATER
Any claims for damage or shortage in shipment must be filed immediately against the transportation company by the consignee.
B. IMPROPER COMBUSTION
C. GAS
Should overheating occur or gas supply fail to shut off, do not turn off or
disconnect electrical supply to the circulator. Instead, shut off the gas supply at
a location external to the appliance.
D. WHEN SERVICING THE BOILER
To avoid electric shock, disconnect electrical supply before performing
maintenance.
To avoid severe burns, allow boiler to cool before servicing.
E. BOILER WATER
Do not use petroleum-based cleaning or sealing compounds in a boiler
system. These products may damage gaskets and seals in the
system. 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 may result.
You must not have a direct connection of the potable water system into the heat exchanger. This could cause flow issues, short cycling,
and an increase of mineral build-up in the unit. This system is designed to have incoming potable water flow through the storage tank
first, then through the heat exchanger. FAILURE TO PIPE THE UNIT PROPERLY WILL VOID THE WARRANTY.
NOTE: Damages resulting from incorrect installation or from use of products not approved by HTP, Inc. ARE NOT covered by warranty.
PART 2 –BEFORE YOU START
VWH units must be connected to a storage tank. Failure to connect the VWH to a storage tank WILL VOID the warranty.
Do not obstruct the flow of combustion and ventilating air. Adequate air must be provided for safe operation. Failure to keep the vent
and combustion air intake clear of ice, snow, or other debris could result in property damage, serious personal injury, or death.

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LP- 446 REV. 9.3.14
Mod Con 500 VWH
Outlet
Temperature
Recovery Gallons Per
Hour
First Hour Rating With 80
Gallon
First Hour Rating With 119
Gallon
First Hour Rating With 175
Gallon
80o
1,410
1,470
1,499
1,535
90o
1,128
1,188
1,217
1,253
100o
940
1,000
1,029
1,065
110o
806
866
895
931
120o
705
765
794
830
130o
627
687
716
752
140o
564
624
653
689
150o
513
573
602
638
160o
470
530
559
595
170o
434
494
523
559
180o
403
463
492
528
Table 1 –Mod Con 500 VWH Recovery Ratings with Storage Tanks and 40oF Inlet Temperature
Mod Con 850 VWH
Outlet
Temperature
Recovery Gallons Per
Hour
First Hour Rating With 80
Gallon
First Hour Rating With 119
Gallon
First Hour Rating With 175
Gallon
80o
2,397
2,457
2,486
2,522
90o
1,918
1,978
2,007
2,043
100o
1,598
1,658
1,687
1,723
110o
1,370
1,430
1,459
1,495
120o
1,199
1,259
1,288
1,324
130o
1,065
1,125
1,154
1,190
140o
959
1,019
1,048
1,084
150o
872
932
961
997
160o
799
859
888
924
170o
738
798
827
863
180o
685
745
774
810
Table 2 –Mod Con 850 VWH Recovery Ratings with Storage Tanks and 40oF Inlet Temperature
Min Tank Size (gal.) = Required Flow (GPM) x 10
Mixing Factor Mf= VWH Outlet Temp –40
70
First Hour Rating = Total VWH Output x VWH Efficiency + .75 x Total Storagex Mf
(VWH Outlet Temp –40) x 8.31
Example:
2 MOD CON VWH 500 Total Output = 1,000,000 BTU @ 94% Efficiency
VWH Outlet Temp 140oF
2 Storage Tanks (80 Gallons Each) Total Storage = 160 Gallons
Mixing factor Mf= 140 –40 = 1.43
70
First Hour Rating = 1,000,000 x .94 + .75 x 160x 1.43
(140 –40) x 8.31
First Hour Rating = 940,000 + 120x 1.43
831
First Hour Rating = 1,131 + 120x 1.43
First Hour Rating = 1,251x 1.43
First Hour Rating = 1789 Gallons
A. WHAT’S IN THE BOX
Also included with the boiler:
Pressure and Temperature Gauge

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LP- 446 REV. 9.3.14
Pressure Relief Valve
Intake PVC Tee with Screens
Exhaust PVC Coupling with Screens
Supply and Return Thermistors
Flow Switch and Fitting
Wiring Harness
System/Pipe Sensor
Installation Manual
Warranty
CSD-1 Form
H-3 Data Sheet
B. HOW BOILER OPERATES
Mod Con VWH®condensing technology intelligently delivers large volumes of hot water while maximizing efficiency by measuring data
from the connected storage tank. Outlined below are the features of the system and how they operate:
Stainless Steel Heat Exchanger - The highly efficient 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.
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.
Control –The integrated control system monitors the system and regulates fan speed to control boiler output. This allows the boiler to
deliver only the amount of heat energy required and nothing more.
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
requires a cascade system sensor and a cascade pump in addition to its own boiler pump. Each of the follower boilers has an individual
pump.
NOTE: When using a system sensor, pipe insulation must be wrapped around it to improve temperature measurement accuracy and
increase overall system efficiency.
System Display and Operational LED Light Indicators –The display allows the user to change the system parameters and monitor
system outputs.
Gas Valve –Senses suction from the blower, allowing gas to flow only if powered and combustion air is flowing.
Integrated Venturi (500 Models) or Swirl Plate (850 Models) –Controls air and gas flow into the burner.
Burner –Constructed of high grade stainless steel, the burner uses premixed air and gas fuel to provide a wide range of firing rates.
Spark Ignition –The burner is ignited by applying high voltage through the system spark electrode. This causes the spark from the
electrode to ignite mixed gas from the burner.
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.
Return Water Temperature Sensor –This sensor monitors the boiler return water temperature (System Return).
Temperature and Pressure Gauge –Allows the user to monitor system temperature and pressure.
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.
Condensation Collection System –This boiler is a high efficiency appliance, therefore the boiler will produce condensate. The
collection system has a float switch which monitors the condensation level and prevents condensation from backing up into the
combustion system. Inside the collection system there is a built in trap which seals the combustion system from the connected drain.
This condensate should be neutralized to avoid damage to the drainage system or piping.

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LP- 446 REV. 9.3.14
Flow Protection –The supplied flow switch is designed to protect the boiler in the event of low flow conditions. The boiler control will
also monitor flow through the heat exchanger by monitoring the return and supply sensor and will shut down the burner before
overheating occurs.
System Pipe Sensor –This sensor is designed to be used in a cascade system. When placed on the supply line feeding the storage
tank, the system pipe sensor measures the temperature of return water and communicates with the control system to modulate the
firing rate of the connected boilers.
Indirect Tank Sensor (optional) –Monitors storage tank temperature.
C. OPTIONAL EQUIPMENT
Below is a list of optional equipment available from HTP:
Indirect Tank Sensor (Part # 7250P-325)
4” Stainless Steel Outside Termination Vent Kit (V2000)
6” Stainless Steel Outside Termination Vent Kit (V3000)
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)
PC Connection Kit (Part # 7250P-320)
Condensate Neutralizer (Part # 7350P-611)
Caster Kit (Part # 7350P-604)
These additional options may be purchased through your HTP distributor.
PART 3 –PREPARE BOILER LOCATION
Carefully consider installation when determining boiler location. Please read the entire manual before attempting installation. Failure to
properly take factors such as boiler venting, piping, condensate removal, and wiring into account before installation could result in
wasted time, money, and possible property damage and personal injury.
A. BEFORE LOCATING THE BOILER
Incorrect ambient conditions can lead to damage to the heating system and put safe operation at risk. Ensure that the boiler installation
location adheres to the information included in this manual. Failure to do so could result in property damage, serious personal injury, or
death.
Failure of boiler or components due to incorrect operating conditions IS NOT covered by product warranty.
1. Installation Area (Mechanical Room) Operating Conditions
Ensure ambient temperatures are higher than 32oF/0oC and lower than 104oF/40oC.
Prevent the air from becoming contaminated by the products, places, and conditions listed in this manual, Part 3, Section F.
Avoid continuously high levels of humidity
Never close existing ventilation openings
The service life of the boiler’s exposed metallic surfaces, such as the casing, as well as internal surfaces, such as the heat exchanger,
are directly influenced by proximity to damp and salty marine environments. In such areas, higher concentration levels of chlorides from
sea spray coupled with relative humidity can lead to degradation of the heat exchanger and other boiler components. In these
environments, boilers must not be installed using direct vent systems which draw outdoor air for combustion. Such boilers must be
installed using room air for combustion. Indoor air will have a much lower relative humidity and, hence, potential corrosion will be
minimized.
This boiler is certified for indoor installations only. Do not install the boiler outdoors. Failure to install this boiler indoors could result in
substantial property damage, severe personal injury, or death.

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LP- 446 REV. 9.3.14
2. Check for nearby connections to:
System water piping
Venting connections
Gas supply piping
Electrical power
Condensate drain
3. Check area around boiler. Remove any combustible materials, gasoline, and other flammable liquids.
Failure to keep boiler area clear and free of combustible materials, liquids, and vapors can result in substantial property damage,
severe personal injury, or death.
4. Gas control system components must be protected from
dripping water during operation and service.
5. If the boiler is to replace an existing boiler, check for and
correct any existing system problems, such as:
System leaks
Location that could cause the system and boiler to
freeze and leak.
Incorrectly-sized expansion tank
6. Clean and flush system when reinstalling a boiler.
NOTE: When installing in a zero clearance location, it may
not be possible to read or view some product labeling. It is
recommended to make note of the boiler model and serial
number.
B. LEVELING AND DIMENSIONS
In order for the condensate to properly flow out of the
collection system, the area where you locate the boiler
must be level. The boiler comes equipped with leveling
feet. Should you find the floor beneath the boiler is uneven,
adjust the leveling feet with a wrench.
Figure 1 –Leveling

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Figure 2 –Dimensions and Specifications

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LP- 446 REV. 9.3.14
C. CLEARANCES FOR SERVICE ACCESS
See Figure 3 for recommended service clearances. If you
do not provide the minimum clearances shown, it might not
be possible to service the boiler without removing it from the
space.
D. RESIDENTIAL GARAGE INSTALLATION
PRECAUTIONS
If the boiler is located in a residential garage, per ANSI
Z223.1:
Mount the bottom of the boiler a minimum of 18”
above the floor of the garage, to ensure the burner and ignition devices are well off the floor.
Locate or protect the boiler so it cannot be damaged by a moving vehicle.
Check with your local Authority Having Jurisdiction for requirements when installing boiler in a garage. Please read the entire manual
before attempting installation. Failure to properly take factors such as boiler venting, piping, condensate removal, and wiring into
account before installation could result in wasted time, money, and possible property damage and personal injury.
E. EXHAUST VENT AND INTAKE PIPE
Vents must be properly supported. The boiler exhaust and intake connections are not designed to carry heavy weight. Vent support
brackets must be within 1’ of the boiler and the balance at 4’ intervals. Venting must be readily accessible for visual inspection for the
first 3’ from the boiler.
The boiler is rated ANSI Z21.13 Category IV (pressurized vent, likely to form condensate in the vent), and requires a special vent
system designed for pressurized venting.
You must also install intake piping from outdoors to the boiler flue adaptor. The resultant installation is categorized as direct vent
(sealed combustion). Note: To prevent combustion air contamination, see Table 3 in this section when considering exhaust
vent and intake pipe termination.
Exhaust vent and intake pipe must terminate near each other and may be vented vertically through the roof or out a side wall. Exhaust
vent and intake piping methods are detailed in the Venting Section. Do not attempt installation using any other means. Be sure to locate
the boiler so exhaust vent and intake piping can be routed through the building and properly terminated. The exhaust vent and intake
piping lengths, routing and termination method must all comply with methods and limits given in the venting section.
F. PREVENT COMBUSTION AIR CONTAMINATION
Install intake piping for the boiler as described in the Venting section. Do not terminate exhaust in locations that can allow
contamination of intake air.
You must pipe outside air to the boiler intake. Ensure that the intake air will not contain any of the contaminants below. For example, do
not pipe intake near a swimming pool. Avoid areas subject to exhaust fumes from laundry facilities. These areas always contain
contaminants. Contaminated air will damage the boiler, resulting in possible substantial property damage, severe personal injury, or
death.
Space must be provided with combustion/ventilation air
openings correctly sized for all appliances located in the
same space as the boiler. The boiler venting cover must
be securely fastened to prevent it from drawing air from
the boiler room. This is particularly important if the boiler is
in a room with other appliances. Failure to comply with the
above warnings could result in substantial property
damage, severe personal injury, or death.
Figure 3 - Clearances

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LP- 446 REV. 9.3.14
PRODUCTS TO AVOID
AREAS LIKELY TO HAVE CONTAMINANTS
Spray cans containing fluorocarbons
Dry cleaning/laundry areas and establishments
Permanent wave solutions
Swimming pools
Chlorinated waxes/cleaners
Metal fabrication plants
Chlorine-based swimming pool chemicals
Beauty shops
Calcium chloride used for thawing
Refrigeration repair shops
Sodium chloride used for water softening
Photo processing plants
Refrigerant leaks
Auto body shops
Paint or varnish removers
Plastic manufacturing plants
Hydrochloric or Muriatic acid
Furniture refinishing areas and establishments
Cements and glues
New building construction
Antistatic fabric softeners used in clothes dryers
Remodeling areas
Chlorine-type bleaches, laundry detergents, and cleaning solvents
Garages and workshops
Adhesives used to fasten building products
Table 3 –Contaminants
NOTE: DAMAGE TO THE BOILER CAUSED BY EXPOSURE TO CORROSIVE VAPORS IS NOT COVERED BY WARRANTY.
(Refer to the limited warranty for complete terms and conditions).
G. REMOVING A BOILER FROM A COMMON VENT SYSTEM
Do not install the boiler into a common vent with any other boiler.
This will cause flue gas spillage or boiler malfunction, resulting in
possible substantial property damage, severe personal injury, or
death.
Failure to follow all instructions can result in flue gas spillage and
carbon monoxide emissions, causing severe personal injury or
death.
When removing an existing boiler, the following steps must be
followed.
1. Seal any unused openings in the common venting system.
2. Visually inspect the venting system for proper size and horizontal
pitch to determine if there is blockage, leakage, corrosion or other defi-
ciencies that could cause an unsafe condition.
3. If practical, close all building doors, windows and all doors between
the common venting system and other spaces in the building. Turn on
clothes dryers and any appliances not connected to the common
venting system. Turn on any exhaust fans, such as range hoods and bathroom exhausts, at maximum speed. Do not operate a summer
exhaust fan. Close all fireplace dampers.
4. Place in operation the appliance being inspected. Follow the lighting instructions. Adjust the thermostat so the appliance will operate
continuously.
5. Test for spillage at the draft hood relief opening after 5 minutes of main burner operation. Use the flame of a match or candle or
smoke from a cigarette.
6. After it has been determined that each appliance remaining connected to common venting system properly vents when tested as
outlined, return doors, windows, exhaust fans, fireplace dampers and any other gas burning appliance to their previous condition of use.
7. Any improper operation of the common venting system should be corrected so the installation conforms to the National Fuel Gas
Code, ANSI Z223.1. When resizing any portion of the common venting system, the common venting system should be resized to
approach the minimum size as determined using the appropriate tables in Appendix G in the National Fuel Gas Code, ANSI Z 223.1.
Figure 4 –CO Warning Label

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LP- 446 REV. 9.3.14
H. UNCRATING AND MOVING BOILER
Uncrating Boiler –Any claims for damage in shipment must be filed immediately against the transportation company by the consignee.
Cold Weather Handling –If boiler has been stored in a very cold location (below 0oF) before installation, handle with care until the
plastic components come to room temperature.
Remove all sides of the shipping crate in order to
allow the boiler to be lifted into its installation
location. Pick the boiler up by the lift rings to avoid
damage to the boiler enclosure. Use either a solid ¾”
diameter black iron pipe or lifting straps to lift the
boiler off of its shipping crate. The boiler is very
heavy. At least two individuals are needed to handle
the boiler properly. If the location is not level, adjust
the boiler’s leveling feet to ensure a level boiler and
proper flow of condensate. If surface flooring is
rough, care should be taken not to catch the leveling
feet and damage the boiler when sliding it into
position.
PART 4 –BOILER PIPING
Failure to follow the instructions in this section WILL VOID the warranty and may result in property damage, serious injury, or death.
Plumbing of this product should only be done by a qualified, licensed plumber in accordance with all local plumbing codes. The boiler is
designed to be connected to a storage tank to supply domestic hot water. HTP offers 80/119/175 gallon size storage tanks in either
Stainless Steel or Glass lined construction. These storage tanks will be directly connected to the Boiler supply and return connection.
A. GENERAL PIPING INFORMATION
The building piping system must meet or exceed the piping requirements in this manual.
The 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.
Use two wrenches when tightening water piping at the appliance. Use one wrench to prevent the appliance return or supply line from
turning. Failure to prevent piping connections from turning could cause damage to appliance components.
B. RELIEF VALVE
Connect discharge piping to a safe disposal location according to the following guidelines.
Never use dielectric unions or galvanized steel fittings when connecting to a stainless steel storage tank or boiler. Failure to follow this
instruction can lead to premature failure of the boiler system. Such failures ARE NOT covered by warranty.
Figure 5 –Lifting the Mod Con

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LP- 446 REV. 9.3.14
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 relief
valve discharge.
Discharge line must be as short as possible and 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, making discharge clearly
visible.
Discharge line shall terminate plain, not threaded, with a material serviceable for temperatures of 375oF or greater.
Do not pipe discharge to any location where freezing could occur.
No shutoff valve may 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 relief valve after filling and pressurizing the 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.
Test relief valve at least once annually to ensure the waterway is clear. If valve does not operate, turn the boiler “off” and call
a plumber immediately.
Take care whenever operating relief valve to avoid scalding injury or property damage.
For boilers installed with only a pressure relief valve, the separate storage vessel must have a temperature and pressure relief
valve installed. This relief valve shall comply with Relief Valves for Hot Water Supply Systems, ANSI Z21.22 CSA4.4.
FAILURE TO COMPLY WITH THE ABOVE GUIDELINES COULD RESULT IN FAILURE OF RELIEF VALVE OPERATION,
RESULTING IN POSSIBILITY OF SUBSTANTIAL PROPERTY DAMAGE, SEVERE PERSONAL INJURY, OR DEATH.
C. SYSTEM WATER PIPING METHODS
EXPANSION TANK AND MAKE-UP WATER
1. Ensure that the expansion tank is sized to correctly handle boiler and system water volume and temperature.
HEATER WATER VOLUME
500 VWH
4.2 Gallons
850 VWH
5.8 Gallons
Table 4
2. The expansion tank must be located as shown in Piping Diagrams, or following recognized design methods. See expansion tank
manufacturer’s instructions for details. Always install an expansion tank designed for potable water systems.
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 an air cushion. An automatic air vent would cause air to leave the system, resulting in improper operation of the expansion tank.
D. CIRCULATOR PUMPS
DO NOT use the boiler circulator in any location other than the ones shown in this manual. The boiler circulator location is selected to
ensure adequate flow through the boiler. Failure to comply with this caution could result in unreliable performance and nuisance
shutdowns from insufficient flow.
The boiler is designed to be connected to a storage tank to supply domestic hot water. HTP offers storage tanks that are 80/119/175
gallon size storage tanks constructed in either stainless steel or glass-lined construction. These storage tanks connect directly to the
boiler supply and return connections. Connect the cold water supply to both the storage bottom port and the supply side of the Mod Con
VWH (shown in Piping details, this section). It is important that you install a flow check on the supply line of Mod Con VWH before you
connect the feed line to the storage tank. This will allow the cold feed to flow through the storage tank first. It is recommended that you
install shut off valves on the cold feed line for ease of future service. If there is a back flow preventer or any type of no return valve in

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LP- 446 REV. 9.3.14
the system, you must install an additional tee for a suitable potable hot water expansion tank. Connect the Storage tank return line to
the return connection located on the Mod Con VWH (shown in Piping Diagrams). Then connect your hot water outlet located on the
storage tank to your hot water plumbing lines.
Never use dielectric unions or galvanized steel fittings when connecting to a stainless steel storage tank or boiler.
When raising tank temperature, you increase the risk of scalding. Use a water tempering or mixing valve and extreme caution. Consult
codes for conformance.
E. SCALDING
When raising tank temperature, you increase the risk of
scalding. Please use a water tempering or mixing valve and
extreme caution when raising tank temperature to lessen
the chance of scalds. Consult codes for conformance.
This water boiler can deliver scalding water at any faucet in
the system. Be careful whenever using hot water to avoid
scalding injury. Certain appliances such as dishwashers and
automatic clothes washers may require increased water
temperature. By setting the thermostat on this water boiler to
obtain the increased water temperature required by these appliances, you may create the potential for scald injury.
To protect against injury, the installer should install a mixing valve in the water system. This valve will reduce point of discharge
temperature by mixing cold and hot water in branch supply lines. Such valves are available from your local plumbing supplier.
Table 5 details the relationship of water temperature and time with regard to scald injury and may be used as a guide in determining the
safest water temperature for your applications.
The table below represents the combined flow rates and pipe sizes when using multiple boilers to design the manifold system for the
primary circuit. To size, simply add up the number of boilers and the required flow rates for the system design temperature. Example:
(5) Mod Con 500 boilers with a design of 30oF temperature rise, with each boiler having an individual flow rate of 33 gpm. To correctly
size the manifold feeding these (5) Mod Con 500 boilers, you would need a pipe size of 4”.
F. HIGH VELOCITY CIRCULATOR PUMP
Every VWH system requires special attention to pump size in order to overcome the pressure drop through the boiler and its related
piping. All circulators installed on the VWH system must be designed for a potable water system.
Water temperature above 140oF requires the circulator pump to run continuously and water hardness between 5 and 7 grains.
Hardness above 7 grains will damage the heat exchanger and shorten the service life of the boiler.
In addition, the heat exchanger has a minimum total water volume that must be taken into account when sizing the circulator. Minimum
flow rates are listed in the table below.
MINIMUM HEATER FLOW RATES
MODEL
MINIMUM FLOW (GPM)
MODCON500VWH
33
MODCON850VWH
54
Table 6 –Minimum Flow Rates
APPROXIMATE TIME /
TEMPERATURE RELATIONSHIPS IN SCALDS
120oF
More than 5 minutes
125oF
1 ½ to 2 minutes
130oF
About 30 seconds
135oF
About 10 seconds
140oF
Less than 5 seconds
145oF
Less than 3 seconds
150oF
About 1 ½ seconds
155oF
About 1 second
Table 5

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LP- 446 REV. 9.3.14
Table 7 –Multiple Boiler Manifold Piping
The table below represents the various system design temperature rise through the Mod Con along with the respective flow and friction
loss which will aid in circulator selection.
SYSTEM TEMPERATURE RISE CHART
20o∆t
25o∆t
30o∆t
MODEL
Friction Feet
Flow GPM
Friction Feet
Flow GPM
Friction Feet
Flow GPM
MODCON500
19
50
11
40
8
33
MODCON850
35
85
26
65
18
54
Table 8 –Temperature Rise Chart

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LP- 446 REV. 9.3.14
Table 9 –Mod Con Heat Exchanger Pressure Drop
G. WATER CHEMISTRY
Chemical imbalance of your water can cause severe damage to your water heater and associated equipment, and may also affect
efficiency. You may have to have your water quality professionally analyzed to determine whether you need to install a water softener.
It is important that the water chemistry on both the domestic hot water and central heating sides are checked before installing the
heater, as water quality will affect the reliability of the system.
Outlined below are those water quality parameters which need to be met in order for the system to operate efficiently for many years.
Failure of a heat exchanger due to lime scale build-up on the heating surface, low pH or other imbalance IS NOT covered by
the warranty.
Water Hardness
Water hardness is mainly due to the presence of calcium and magnesium salts dissolved in the water. The concentration of these salts
is expressed in mg/L, ppm or grains per gallon, as a measure of relative hardness of water. Grains per gallon is the common reference
measurement used in the U.S. water heater industry. Hardness expressed as mg/L or ppm may be divided by 17.1 to convert to grains
per gallon. Water may be classified as very soft, slightly hard, moderately hard, or hard based on its hardness number. The minerals in
the water precipitate out when the water is heated and cause accelerated lime and scale accumulation on a heat transfer surface.
If the hardness of the water exceeds the maximum level of 7 grains per gallon, water should be softened to a hardness level no lower
than 5 grains per gallon. Water softened as low as 0 to 1 grain per gallon may be under-saturated with respect to calcium carbonate,
resulting in water that is aggressive and corrosive.
pH of Water
pH is a measure of relative acidity, neutrality or alkalinity. Dissolved minerals and gases affect water pH. The pH scale ranges from 0 to
14. Water with a pH of 7.0 is considered neutral. Water with a pH lower than 7 is considered acidic. Water pH higher than 7 is
considered alkaline. A neutral pH (around 7) is desirable for most potable water applications. Corrosion damage and heater failures
resulting from water pH levels of lower than 6 or higher than 8 ARE NOT covered by the warranty. The ideal pH range for water
used in a storage tank or a water heater system is 7.2 to 7.8.
Total Dissolved Solids
Total Dissolved Solids (TDS) is a measurement of all minerals and solids dissolved in a water sample. The concentration of total
dissolved solids is usually expressed in parts per million (ppm).

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LP- 446 REV. 9.3.14
Water with a high TDS concentration will greatly accelerate lime and scale formation in the hot water system. Most high TDS
concentrations precipitate out of the water when heated. This can generate a scale accumulation on the heat transfer surface that will
greatly reduce the service life of a water heater. This scale accumulation can also impede the ability of the heat exchanger to transfer
heat into the water. A heat exchanger damaged or blocked by lime/scale accumulation must be replaced.
The manufacturer of the water heater has no control of water quality, especially TDS levels in your system. Total dissolved solids in
excess of 2,000 ppm will accelerate lime and scale formation in the heat exchanger. Heat exchanger failure due to total dissolved solids
in excess of 2,000 ppm is a non-warrantable condition. Failure of a water heater due to lime scale build up on the heating surface
IS NOT covered by the warranty.
Hardness: 7 grains
Chloride levels: 100 ppm
pH levels: 6-8
TDS: 2000 ppm
Sodium: 20 mGL
*NOTE: It is recommended you clean heat exchanger at least once a year to prevent lime scale buildup. Follow the maintenance
procedure to clean the heat exchanger in the Maintenance Section (Part 12 of this manual).
Piping components
Water heating system piping:
Water boiler system piping MUST be sized per technical pipe requirements listed in Table 7. Reducing pipe size can restrict flow rate
through the boiler, causing inadvertent short cycling and poor system performance.
Check valves:
Field supplied. Check valves are recommended for installation as shown in Piping Details.
Water boiler isolation valves:
Field supplied. Full port ball valves are required. Failure to use full port ball valves could result in a restricted flow rate through the water
boiler.
Anti-scald mixing valve:
Field supplied. A thermostatic mixing valve is recommended when storing domestic hot water above 115°F.
Unions:
Field supplied: Recommended for unit serviceability. DO NOT USE DIELECTRIC UNIONS!
ONLY BRASS, COPPER, OR STAINLESS STEEL.
Pressure relief valve:
Factory supplied on VWH. The pressure relief valve is sized to ASME specifications. Storage tank may require additional relief valves
depending on local codes.