A. O. Smith VB-1500 Service Manual
500 Tennessee Waltz Parkway
Ashland City, TN 37015
Service Handbook
COMMERCIAL GAS FIRED BOILER
FOR MODELS:
VW/VB 1500, VW/VB 2000
HOT WATER SUPPLY
HYDRONIC HEATING
SERIES 100, 101
INSTALLATION CONSIDERATIONS - PRE SERVICE
CHECKS - WATER HEATER CONSTRUCTION -
OPERATION & SERVICE - TROUBLESHOOTING
SERVICING SHOULD ONLY BE PERFORMED BY A QUALIFIED SERVICE AGENT
PRINTED IN THE U.S.A. 0910 318149-000
TABLE OF CONTENTS
TABLE OF CONTENTS .......................................................................... 1
INTRODUCTION .................................................................................... 2
Model Numbers And Factory Congurations ..................................... 2
Qualications ..................................................................................... 2
Qualied Installer or Service Agency .......................................... 2
Service Warning ................................................................................2
Service Reminder .............................................................................. 3
Tools Required ................................................................................... 3
INSTALLATION CONSIDERATIONS ..................................................... 4
Instruction Manual .............................................................................4
Closed Water Systems ...................................................................... 4
Thermal Expansion ............................................................................ 4
Air Requirements ............................................................................... 4
Contaminated Air ............................................................................... 4
Venting ............................................................................................... 5
Water Piping ...................................................................................... 5
Temperature Rise & Flow Rate .......................................................... 5
Bypass Lines .....................................................................................5
Boiler Controls ................................................................................... 6
The Heating Cycle ....................................................................... 6
Primary System Control .............................................................. 6
Remote Temperature Probe Installation ...................................... 7
The Controlling Probe ................................................................. 7
FEATURES AND COMPONENTS ......................................................... 8
Front, Back & Side Views .................................................................. 8
How It Works .....................................................................................9
OPERATION AND SERVICE ............................................................... 10
Modulating Fire Operation ............................................................... 10
Combustion Blower ......................................................................... 10
Burner Assembly ..............................................................................11
Venturi & Gas Train ......................................................................... 12
Cong Key ....................................................................................... 13
Combustion Blower Speed Data ..................................................... 14
Temperature Probes ........................................................................ 15
Inlet and Outlet Temperature Probes ........................................ 15
Remote Temperature Probe ...................................................... 15
Quad Thermistor Probe ............................................................. 15
Control Panel ................................................................................... 17
Pressure Switches ........................................................................... 18
MCB - Modulation Control Board ..................................................... 19
PDB - Power Distribution Board ...................................................... 28
Power Supply Test ........................................................................... 33
START UP ............................................................................................ 34
Prior To Start Up .............................................................................. 34
Modulate Mode ............................................................................... 34
Modulate Mode Adjustment ....................................................... 34
Turning The Boiler Off......................................................................34
Start Up Procedure .......................................................................... 35
Manifold Gas Pressure Test............................................................. 38
CONTROL SYSTEM OPERATION ...................................................... 39
EMC 5000 Modulation Control ........................................................ 39
Control System Features: ......................................................... 39
Control System Navigation .............................................................. 40
UIM - User Interface Module ..................................................... 40
Status Lights ............................................................................. 41
Firing Rate Status ..................................................................... 41
User Input Buttons .................................................................... 42
Adjusting User Settings ...................................................................43
Operating Setpoint Adjustment ................................................. 43
Control System Menus ....................................................................44
Sequence Of Operation ................................................................... 45
TROUBLESHOOTING ......................................................................... 46
Poor Combustion - Ignition Failure - Rough Start/Operation ........... 46
Verify Correct Cong Key Is Installed ........................................ 46
Adequate Combustion Air - Proper Venting .............................. 46
Vent Gas Recirculation .............................................................. 46
Restore Gas Flow Settings To Default ...................................... 47
Firing Rate - Modulation Performance ...................................... 47
Burner Inspection ...................................................................... 47
Error Messages ...............................................................................48
LCD Display Is Blank ................................................................ 49
Display Fail ................................................................................ 50
No Cong Key ........................................................................... 50
Cong Key CRC ........................................................................ 50
Cong Key Part ......................................................................... 51
Low AC Voltage ......................................................................... 51
Low 24 VAC .............................................................................. 51
Low Water ................................................................................. 52
MRHiLimit .................................................................................. 52
Low Gas .................................................................................... 53
No Flow ..................................................................................... 54
Inlet Probe ................................................................................. 56
Tank Probe ................................................................................ 57
Outlet Probe .............................................................................. 58
Igniter ........................................................................................ 58
Blower Prover ............................................................................ 59
Blocked Inlet .............................................................................. 61
Blocked Flue ............................................................................. 62
Flame ........................................................................................ 63
PIPING DIAGRAMS ............................................................................. 65
Temperature Probe and Bypass Line Location ......................... 65
BOILER TEMPERATURE LOGS ......................................................... 69
Scheduling Deliming Maintenance ............................................ 69
Servicing should only be performed by a Qualied Service Agent
1
INTRODUCTION
This Service Manual covers VF Boiler models VW/VB 1500 and VW/VB 2000 - Series 100/101 Boilers. The
instructions and illustrations contained in this Service Manual will provide you with troubleshooting procedures
to diagnose and repair common service problems and verify proper operation.
MODEL NUMBERS AND FACTORY CONFIGURATIONS
See the rating plate afxed to the Boiler for Model, Series and Serial numbers. The VF product name stands
for Variable Fire. The VF Boiler model numbers are expressed on the boiler rating plates as: VW 1500, VW
2000, VB 1500, and VB 2000. The 1500 models are rated at 1,500,000 Btu/hr and the 2000 models are rated
at 2,000,000 Btu/hr. The two different model number prexes, VW and VB, are used to indicate the factory
congurations as follows:
• VW model Boilers are factory congured for domestic hot water system requirements.
• VB model Boilers are factory congured for hydronic heating system requirements.
VW and VB factory congurations differ in three respects:
1. Factory installed all bronze Boiler Circulation Pump:
• VW Models standard.
• VB Models optional.
2. Factory installed pressure only relief valve:
• VW Models 125 PSI valve standard.
• VB Models 50 PSI valve standard.
3. Temperature Setting Range:
• VW Models
• Operating Setpoint: 105°F to 190°F (41°C to 88°C).
• Automatic Reset High Limit: 135°F to 210°F (57°C to 99°C).
• VB Models
• Operating Setpoint: 105°F to 215°F ((41°C to 102°C).
• Automatic Reset High Limit: 135°F to 235°F (57°C to 113°C).
Note: VW models can be special ordered without the factory installed pump and VB models can be special
ordered with a factory installed pump. These factory congurations can also be changed in the eld by
installing circulation pumps, changing pressure relief valves and dip switch settings on Control System circuit
boards to accommodate domestic and hydronic hot water system requirements, see MCB - Section D on
page 23 and Field Supplied Boiler Circulation Pumps on page 30.
QUALIFICATIONS
QUALIFIED INSTALLER OR SERVICE AGENCY
Service of VF Boilers requires ability equivalent to that of a Qualied Service Agent (dened by ANSI below) in
the eld involved. Installation skills such as plumbing, air supply, venting, gas supply and electrical supply are
required in addition to electrical testing skills. Start up and servicing of VF Boilers also requires combustion
analysis skills and test equipment.
ANSI Z223.1 2006 Sec. 3.3.83: “Qualied Agency” - “Any individual, rm, corporation or company that either
in person or through a representative is engaged in and is responsible for (a) the installation, testing or
replacement of gas piping or (b) the connection, installation, testing, repair or servicing of appliances and
equipment; that is experienced in such work; that is familiar with all precautions required; and that has
complied with all the requirements of the authority having jurisdiction.”
SERVICE WARNING
If you are not qualied (as dened by ANSI above) and licensed or certied as required by the authority
having jurisdiction to perform a given task do not attempt to perform any of the procedures described in
this manual. If you do not understand the instructions given in this manual do not attempt to perform any
procedures outlined in this manual.
2
Servicing should only be performed by a Qualied Service Agent
SERVICE REMINDER
When performing any troubleshooting step outlined in this Service Manual, always consider the wiring and
connectors between components. Perform a close visual inspection of all wiring and connectors to and from
a given component before replacing components. Ensure wires were stripped before being crimped in a wire
connector, ensure wires are crimped tightly in their connectors, ensure connection pins in sockets and plugs
are not damaged or worn, ensure plugs and sockets are mating properly and providing good contact.
Failure to perform this critical step or failing to perform this step thoroughly often results in needless down
time, unnecessary parts replacement, and customer dissatisfaction.
TOOLS REQUIRED
• Instruction Manual that came with the Boiler.
• Hand tools common to installation and service of commercial water heaters and boilers.
• TORX® T40 or 5 mm hex wrench - for setting gas mixture at gas valve.
• 3 mm or 7/64 inch hex (Allen) wrench - for setting gas mixture at gas valve.
• Two Manometers or Pressure Gauges
• One - U tube manometer or gauge for measuring supply gas pressure.
• One (optionally two) digital Manometer(s) range -15.00 to +15.00" W.C., resolution 0.01" W.C.
Recommend UEI model EM200, TPI model 620 or equivalent. Used to measure manifold gas
pressures and to test performance of pressure switches. Optional second digital manometer can be
used in place of U tube manometer for measuring supply gas pressures.
• 1/4" and 3/8" plastic/silicone/rubber exible tubing - used to connect manometers to pressure sensing
ports on Boiler during start up and service.
• 1/4" and 3/8" plastic barbed Tee tting - standard automotive emission grade ttings - used to connect
manometers to pressure sensing ports on Boiler during start up and service.
• True RMS Digital Multi Meter DMM, recommend UEI model DL289 or Fluke equivalent. Capable of
measuring:
• AC/DC Voltage
• Ohms
• DC micro amps μA (ame sensing current)
• AC amp meter- recommend UEI model DL289 or equivalent.
• Combustion analyzer capable of measuring:
• CO2 (carbon dioxide)
• CO (carbon monoxide)
• Draft Pressure
• Exhaust Temperature (vent gases)
Servicing should only be performed by a Qualied Service Agent
3
INSTALLATION CONSIDERATIONS
This section of the Service Manual covers some of the critical installation requirements that, when overlooked,
often result in operational problems, down time and needless parts replacement. Costs to correct installation
errors are not covered under the limited warranty. Ensure all installation requirements and instructions
contained in the Instruction Manual that came with the Boiler have been followed prior to performing any
service procedures.
INSTRUCTION MANUAL
Have a copy of the Instruction Manual that came with the Boiler on hand for the Model and Series number
being serviced. Installation information given in this Service Manual is not a complete installation instruction.
Installation information given in this manual has a limited focus as it applies to servicing the Boiler. This
Service Manual does not replace or supersede the Instruction Manual that came with the Boiler. Always refer
to the Instruction Manual for complete installation instructions. If the Instruction Manual is not on hand, copies
can be obtained from the manufacturers web site or by calling the toll free support phone number shown on
the back cover of this manual.
CLOSED WATER SYSTEMS
Water supply systems may, because of code requirements or such conditions as high line pressure, among
others, have installed devices such as pressure reducing valves, check valves, and back ow preventers.
Devices such as these cause the water system to be a closed system.
THERMAL EXPANSION
As water is heated, it expands (thermal expansion). In a closed system the volume of water will grow when
it is heated. As the volume of water grows there will be a corresponding increase in water pressure due to
thermal expansion. Thermal expansion can cause premature tank failure (leakage). This type of failure is not
covered under the limited warranty. Thermal expansion can also cause intermittent Temperature-Pressure
Relief Valve operation; water discharged from the valve due to excessive pressure build up. This condition
is not covered under the limited warranty. The Temperature-Pressure Relief Valve is not intended for the
constant relief of thermal expansion.
A properly sized thermal expansion tank must be installed on all closed systems to control the harmful effects
of thermal expansion. Contact a local plumbing service agency to have a thermal expansion tank installed.
AIR REQUIREMENTS
Carefully review the requirements for combustion and ventilation air in the Instruction Manual that came with
the Boiler. Failure to meet these requirements when the Boiler is installed or overlooking their importance
when servicing the Boiler often results in needless down time, unnecessary parts replacement, and customer
dissatisfaction.
An inadequate supply of air for combustion and ventilation often causes operational problems. A lack of
combustion and ventilation air can create a negative ambient air pressure in the installed space which can
lead to improper combustion and operational problems with pressure switches.
CONTAMINATED AIR
Combustion air that is contaminated can greatly diminish the life span of the Boiler and its components such
as Igniters and Burners. Propellants of aerosol sprays, beauty shop supplies, water softener chemicals and
chemicals used in dry cleaning processes that are present in the combustion, ventilation or ambient air can
cause such damage.
Vapors from volatile compounds such as solvents, cleaners, chlorine based chemicals and refrigerants in
addition to being highly ammable in many cases, can also react to form highly corrosive substances such as
hydrochloric acid inside the combustion chamber. The results can be hazardous and cause product failure.
If the Boiler is installed in laundries with dry cleaning equipment, it is imperative the Boiler be installed in a
Direct Vent conguration so that air for combustion is derived directly from the outdoor atmosphere through a
sealed intake air pipe. See the venting installation section in the Instruction Manual that came with the Boiler
for more information on Direct Vent installations.
4
Servicing should only be performed by a Qualied Service Agent
VENTING
Ensure all venting requirements and venting installation instructions contained in the Instruction Manual that
came with the Boiler have been observed and followed. Failing to install the required Boot Tee tting at the
Boiler's vent connection, not installing the factory provided vent and/or intake air terminations, exceeding
the maximum equivalent vent and/or intake air piping lengths, adding too many elbows to the intake air
and/or vent pipes, installing the wrong vent/intake air pipe size, will cause operational problems, improper
combustion, rough starting/operation and Control System lock outs.
WATER PIPING
Ensure all water piping requirements, diagrams and piping installation instructions contained in the Instruction
Manual that came with the Boiler have been observed and followed. Factory installed pumps on VF Boilers
are sized for up to a maximum of 25 equivalent feet of outlet (supply) and inlet (return) piping; 50 equivalent
feet total. Exceeding these limitations will lead to Control System lock outs and can permanently damage the
Boiler's Heat Exchanger. A bypass line must be installed between the outlet and inlet piping of the Boiler on
the "system side" of the Boiler's Circulation Pump to prevent condensation on the copper Heat Exchanger,
see the Piping Diagrams beginning on page 65.
TEMPERATURE RISE & FLOW RATE
Water ow rates through the Boiler are critical, ow rates
Ou t let
In l et
De l ta T
=
Tank
in the eld. Because the temperature rise through the Boiler is directly linked to the ow rate and is simple to
measure, temperature rise is commonly used to conrm proper ow rates.
Temperature rise is calculated by subtracting the inlet water temperature from the outlet water temperature.
Temperature rise is commonly referred to as the "Delta T" and expressed as ΔT. The temperature rise through
the Boiler should be set between 20° F and 30°F. Temperature rise (ow rate) is set by throttling a ow control
valve installed in the Boiler's outlet (supply) water line with the boiler ring at 100%, see Figure 33 on page
65. Never attempt to throttle the outlet valve unless the Boiler is ring at 100%. Valves on the Boiler's inlet
(return) water line must never be throttled and left fully open at all times except when servicing the Boiler.
The Outlet, Inlet and Delta T (ΔT) are all displayed on the Control System's default Temperatures Menu. The
Control System is programmed to warn the end user whenever the temperature rise is below 20° F by slowly
ashing on and off "< 20" to the right of Delta T on the default Temperatures Menu. See the illustration above.
14 0 °F
12 5 °F
15 ° F
11 5 °F
<2 0
<< < <
that are too low may cause excessive lime/calcium
accumulation inside the Heat Exchanger while ow rates
that are too high can lead to velocity erosion that can
eventually cause water leaks. Boiler efciency is also
affected by ow rates. Measuring the actual water ow rate
(gallons per minute) through the Boiler is often impractical
BYPASS LINES
Bypass lines are required on all VF Boiler installations to
Ou t let
In l et
De l ta T
=
Tank
outlet (supply) and inlet (return) water lines, see Figure 33 on page 65. After the temperature rise through the
Boiler has been set the ow control valve in the bypass line is throttled to ensure a minimum 120° F inlet
water temperature with the Boiler ring at 100%. Never attempt to throttle the bypass valve unless the Boiler
is ring at 100%.
Some condensate formation on a cold start up is normal. However, if condensate formation is not prevented
during normal operating conditions, copper oxide will form on the Heat Exchanger and will eventually block
the ow of ue gases through the Heat Exchanger. The Control System is programmed to warn the end user
whenever the inlet water temperature is below 120° F by slowly ashing on and off "< 120" to the right of Inlet
water temperature on the default Temperatures Menu. See the illustration above.
14 0 °F
11 5 °F
<1 2 0
25 ° F
11 5 °F
Servicing should only be performed by a Qualied Service Agent
<< < <
maintain a minimum inlet water temperature of 120°F.
Bypass lines feed a portion of the outlet water back to the
inlet of the Boiler which raises the inlet water temperature
and helps prevent condensate formation on the copper
Heat Exchanger, see Figure 3 on page 9. Bypass lines are
installed with a ow control valve between the Boiler's
5
BOILER CONTROLS
Boiler controls that are improperly installed or congured can cause serious operational and service related
problems such as short cycling. This section provides information for how various controls can work together
or independently to provide proper boiler and system control.
THE HEATING CYCLE
Two conditions must be met before the VF Boiler can start a heating cycle:
1. The actual temperature sensed by the Control System from the designated "Controlling Probe" (page 7)
must be lower than the Operating Setpoint minus the Setpoint Differential, see Adjusting User Settings
on page 43.
2. The Enable/Disable circuit must be a closed circuit. There are two wires provided in the wiring junction
box on the back of the Boiler for this circuit, see Figure 1.
NOTE: See the Sequence Of Operation on page 45.
PRIMARY SYSTEM CONTROL
All VF Boiler installations require a “Primary System Control” that senses and reacts to water temperature
inside the storage tank on domestic water applications or in the return line on primary/secondary hydronic
heating systems. When installed and congured properly the Primary System Control will activate and
deactivate boiler heating cycles based on its setpoint compared to current system water temperature. There
are three suitable methods to congure a Primary System Control. One of the following three methods MUST
BE used.
POWER SUPPLY AND SYSTEM CONTROL - FIELD WIRING
120 VAC
INPUT
POWER
SUPPLY
FACTORY SUPPLIED REMOTE
TEMPERATURE PROBE OR QUAD
THERMISTOR PROBE
FIELD SUPPLIED
EXTERNAL CONTROL
120 VAC HOT
120 VAC NEUTRAL
GND - EARTH GROUND
COM
NO
JUNCTION BOX
BACK OF BOILER
HIGH VOLTAGE
WIRING
LOW VOLTAGE
CONTROL WIRING
Figure 1
FACTORY INSTALLED WIRING
FIELD INSTALLED WIRING
BLACK - 120 VAC HOT
WHITE - 120 VAC NEUTRAL
GREEN - GROUND
YELLOW - 5 VDC
YELLOW - 5 VDC
BLACK/WHITE STRIPE - 24 VAC
YELLOW/VIOLET STRIPE - 24 VAC
REMOTE
TEMP
PROBE
ENABLE
DISABLE
CIRCUIT
1. The Primary System Control can be the Boiler’s EMC 5000 Control System working with the factory
supplied Remote Temperature Probe or the optional Quad Thermistor Probe installed inside the storage
tank on domestic water applications or in the return line on primary/secondary hydronic heating systems.
This application ensures the Boiler’s ability to fully modulate its ring rate. See Temperature Probes on
page 15 and Figure 33 on page 65.
2. Alternatively, the iCOMM™ system hardware working with an onsite BACnet compliant BMS (Building
Management System) can be used as a Primary System Control. This application ensures the Boiler’s
ability to fully modulate its ring rate and allows BACnet compliant controls to utilize outdoor temperature
6
Servicing should only be performed by a Qualied Service Agent
reset schedules to maximize energy savings on hydronic heating applications during medium and low
load conditions. The onsite BACnet compliant BMS must have its own temperature sensor installed in the
storage tank for domestic water applications or in the return line on primary/secondary hydronic heating
systems or it must monitor the factory supplied Remote Temperature Probe or Quad Thermistor Probe
as described in the rst method to initiate boiler heating cycles. iCOMM™ system hardware is purchased
separately from the manufacturer. For more information call 888 928-3702.
3. The Primary System Control may also be a eld supplied external control such as a storage tank
thermostat or boiler sequencing panel. Field supplied external controls must meet three requirements to
be a suitable Primary System Control:
A. The eld supplied control must be able to sense water temperature inside the storage tank on
domestic water applications or in the return loop on primary/secondary hydronic heating systems.
B. The eld supplied control must function as a thermostat with a set of “dry” (no voltage or load)
control contacts to use with the Boiler’s Enable/Disable circuit, see Figure 1 on page 6 for wiring.
C. The eld supplied control must open/close its control contacts based on actual system
temperature AND its own system temperature setpoint.
FIELD SUPPLIED CONTROL NOTES: If the eld supplied external control does not meet all three of the
requirements listed above it MUST NOT be used as the required Primary System Control.
When using a eld supplied external control as the Primary System Control the Operating Setpoint
of Boiler Control System must be set at least 5° higher than the system setpoint of the eld supplied
control. This is done to ensure the Boiler’s setpoint does not deactivate the current heating cycle before
the external control’s setting has been satised. This also prevents the Boiler from short cycling. See
Adjusting User Settings on page 43.
When a eld supplied external control is used as the Primary System Control it activates and deactivates
boiler operation based on the temperature it senses in the system. It cannot control the Boiler’s ring rate.
The Boiler is not able to modulate its ring rate when using this type of Primary System Control.
REMOTE TEMPERATURE PROBE INSTALLATION
All VF Boilers are supplied from the factory with a Remote Temperature Probe which is suitable for all single
boiler applications, see Figure 8 on page 15. When connecting up to 4 boilers to a single storage tank or one
primary/secondary hydronic heating system the optional Quad Thermistor Probe should be used, see Figure
9 on page 16. Call the toll free parts department phone number on the back of this manual to order the Quad
Thermistor Probe.
On domestic hot water applications the Remote Temperature Probe or the optional Quad Thermistor Probe
MUST BE installed in the designated temperature control opening on the storage tank, typically a 3/4 inch
NPT opening in the lower portion of the tank. On hydronic heating applications the probe being used MUST
BE installed in the return line of the primary hydronic heating loop before (upstream) the rst boiler. A eld
supplied Tee tting with a 3/4 inch NPT branch is installed in the return line for this purpose. See Figure 33
on page 65 and the piping diagrams in the back of this manual for probe location.
Once the probe has been installed in the system, see the Field Wiring section in the Installation Manual that
came with the Boiler and Figure 1 on page 6 in this manual for wiring instructions.
THE CONTROLLING PROBE
When the Remote Temperature Probe or the optional Quad Thermistor Probe and the eld wiring has been
installed the probe being used must be designated as the “Controlling Probe." To do this turn off power to the
Boiler and locate the SW1 dipswitch array on the MCB circuit board, see Figure 12 on page 19 and Figure 16
on page 23.
SW1 dipswitch #4 must be set to the “On” position to congure the Remote Temperature Probe or the
optional Quad Thermistor Probe as the Controlling Probe. The SW1 dipswitch #4 is set to “Off” from the
factory so this change must be performed on all installations. When power to the Boiler is turned back on the
Boiler’s Control System will now monitor the remote probe that was installed and use temperature data from
that probe to activate and deactivate heating cycles and to modulate the ring rate of the Boiler. See Table 4
on page 23 to congure the SW1 dipswitches.
Servicing should only be performed by a Qualied Service Agent
7
FEATURES AND COMPONENTS
FRONT, BACK & SIDE VIEWS
FRONT VIEW
TOP FRONT PANEL
OPENS FOR SERVICE
Outlet
155°F
Inlet
125°F
-
Delta T
30°F
=
Tank
120°F <<<<
Select
Up
Menu
25% Firing Rate 100%
Down
Help
UIM
(User Interface Module)
Service Standby Running
BACK VIEW
1 1/4 INCH NPT SUPPLY GAS
CONNECTION WITH FACTORY
INSTALLED SHUTOFF VALVE
WITH SUPPLY GAS TEST PORT
VF
WIRING/ELECTRICAL
JUNCTION BOX
PRESSURE ONLY RELIEF VALVE
VW MODELS - 125 PSI
VB MODELS - 50 PSI
2 1/2 INCH NPT OUTLET
WATER CONNECTION WITH
OEM TEE FITTING INSTALLED
WITH PRESSURE RELIEF
VALVE AND FLOW SWITCH
VENT (EXHAUST)
CONNECTION
7 INCH - AL29-4C
STAINLESS STEEL
FLOW
SWITCH
VENTILATION
AIR OPENINGS
INTAKE AIR
CONNECTION
6 INCH PVC
2 1/2 INCH NPT
INLET WATER
CONNECTION
VENTILATION
AIR OPENINGS
CONDENSATE
DRAIN HOSE
OPENING
SIDE VIEW
1 1/4 INCH NPT SUPPLY GAS
CONNECTION WITH FACTORY
INSTALLED SHUTOFF VALVE
WITH SUPPLY GAS TEST PORT
PRESSURE ONLY RELIEF VALVE
125 PSI ON VW MODELS
50 PSI ON VB MODELS
ALL BRONZE BOILER CIRCULATION PUMP
FACTORY INSTALLED AT INLET WATER
CONNECTION:
VW MODELS - STANDARD
VB MODELS - OPTIONAL
VENT (EXHAUST)
CONNECTION
7 INCH - AL29-4C
STAINLESS STEEL
Figure 2
8
Servicing should only be performed by a Qualied Service Agent
HOW IT WORKS
L
L
VF Boiler Heat Exchangers are ASME constructed and rated at 160 PSI. All VF Boilers are SCAQMD Rule
1146.2 low NOx compliant and are equipped with CSD-1 compliant controls. The Heat Exchanger is a circular
shaped vertical tube 4 pass Heat Exchanger constructed from 30 extruded copper tubes roll tted into two
ASME grade steel multiple pass headers that are glass lined.
Water enters the upper header through the inlet water connection and travels down and up a total of 4 times
through the copper tubes and headers. Steel vertical ue bafes are secured to the copper tubes to regulate
the ow of ue gases.
The Heat Exchanger is housed in a sealed stainless steel combustion chamber to contain the products of
combustion and properly convey ue gases to the vent/exhaust connection on the back of the boiler. This
combustion chamber design prevents critical boiler components from being exposed to high temperature ue
gases. The boiler cabinet is constructed with multiple panels that can be removed during operation for inspection.
HEAT EXCHANGER / COMBUSTION BLOWER & BURNER VIEWS
COMBUSTION
BLOWER
DRAIN
VALVE
COMPLETE ASSEMBLY HEAT EXCHANGER
COMBUSTION
GAS VALVE
VENTURI
CONDENSATE
TRAY
ASME GRADE
AIR INTAKE
STAINLESS STEEL
HEAT EXCHANGER
ENCLOSURE
VENT/EXHAUST CONNECTION
7 INCH AL29-4C STAINLESS STEEL
STEEL GLASS
LINED HEADERS
DRAIN
VALVE
COMBUSTION
STEEL RADIAL
FIRE BURNER
BLOWER
ADAPTER
INLET WATER
CONNECTION
OUTLET WATER
CONNECTION
30 EXTRUDED
COPPER FIN
VERTICA
WATER TUBES
WITH STEE
FLUE BAFFLES
BLOWER
BLOWER
ADAPTER
STAINLESS
BLOWER/BURNER ASSEMBLY
Figure 3
Servicing should only be performed by a Qualied Service Agent
9
OPERATION AND SERVICE
MODULATING FIRE OPERATION
VF Boilers are modulating re boilers, the Control Systems modulates the ring rate of the Burner between
25% and 100% to match system load by controlling the speed of the Combustion Bower, see Figure 4.
VF Boilers do not have a gas orice. The Combustion Blower "pulls" fuel gas from the outlet of the 120 VAC
Gas Valve (when energized) into a Venturi that is connected to the inlet of the Combustion Blower, see Figure
6 on page 12. The ring rate of the Boiler is directly proportional to the speed of the Combustion Blower motor.
As the blower speed increases, the pressure inside the Venturi falls creating a stronger vacuum which pulls
more fuel gas into the blower/burner assembly which increases the ring rate.
The Control System controls the speed of the Combustion Blower in response to system temperature. As the
system temperature falls blower speed is increased to provide more heating capacity. The Control System
sends digital speed instructions to the electronic speed control which is part of the Combustion Blower
assembly, see Figure 4 on page 10.
COMBUSTION BLOWER
The Combustion Blower is an assembly that includes the blower motor, housing and an integral electronic
speed control. The PDB (Power Distribution Board - see page 28) sends 120 VAC and an earth ground from
its J3 socket to the 120 VAC 3 pin socket on the Combustion Blower assembly to power the electronic speed
control. The MCB (Modulation Control Board - see Figure 12 on page 19) sends an instruction to start, stop and
control the blower motor speed. Four wires from the J24 socket on the MCB (see page 27) carry this instruction
to the 5 pin socket on the Combustion Blower assembly, see Figure 4 below.
LIFT
HANDLE
BLOWER MOTOR
WITH INTEGRATED
ELECTRONIC SPEED
CONTROL
COMBUSTION BLOWER
BLOWER
HOUSING
120 VAC POWER
3 PIN SOCKET
MCB SPEED
INSTRUCTION
5 PIN SOCKET
10
BLOWER
OUTLET FLANGE
Figure 4
Servicing should only be performed by a Qualied Service Agent
BURNER ASSEMBLY
The Burner on the VF Boiler is a stainless steel radial re burner with a woven steel ber surface. It is installed
in the center of the vertical tube Heat Exchanger, see Figure 3 on page 9. The Burner is mounted inside the
recess of the top header on the Heat Exchanger. A Blower Adapter is installed between the Combustion
Blower's condensate tray and the Burner, see Figure 5 below.
The Igniter on the VF Boiler is a 120 VAC hot surface igniter. The Igniter receives power from the J18 socket
on the MCB (Modulation Control Board - see page 22). Normal resistance of the Igniter is 40-70 ohms @ 77° F
(25° C). The Control System monitors current through the Igniter and must sense a minimum of 2.7 AC amps
before it will energize the 120 VAC Gas Valve.
A Low Gas Pressure Switch is installed in the body of the 120 VAC Gas Valve. This is a normally open switch
that closes on a rise in pressure. Switch contacts close at +4.0" W.C. on natural gas models and +6.4" W.C.
on propane gas models.
VF Boilers have two Flame Sensors. One Flame Sensor is mounted close to the Burner to sense ame at
lower ring rates; the second Flame Sensor is mounted further away to sense ame at higher ring rates,
see Figure 5 below. A single wire, connected the J16 spade connector (see page 22) on the MCB, is bifurcated
(divided) into two wires, each end then connects to one of the two Flame Sensors. The Control System must
sense a minimum of 2.5 DC micro amps (2.5 µA) to prove ame at the Burner.
COMBUSTION
BLOWER
NOTE: BLOWER
ASSEMBLY INCLUDES
INTEGRATED
ELECTRONIC SPEED
CONTROL.
120 VAC
GAS VALVE
CONDENSATE
TRAY
BLOWER
ADAPTER
TWO FLAME SENSORS
FIRST FLAME SENSOR MOUNTED
CLOSE TO BURNER TO SENSE
FLAME DURING LOW FIRE.
SECOND FLAME SENSOR
MOUNTED FURTHER FROM
BURNER TO SENSE FLAME
DURING HIGH FIRE.
GASKETS
NOTE: 40-70 OHMS @ 77° F
(25°C). CONTROL SYSTEM
MUST SENSE A MINIMUM
OF 2.7 AC AMPS BEFORE
ENERGIZING GAS VALVE
VF BOILER STAINLESS
STEEL BURNER
LOW GAS
PRESSURE
SWITCH
NOTE: N.O. SWITCH
CLOSE ON RISE
+4.0” W.C. NATURAL
+6.4” W.C. PROPANE
120 VAC
HOT SURFACE
IGNITER
RADIAL FIRE
STAINLESS
STEEL BURNER
NOTE: CONTROL SYSTEM MUST SENSE A
MINIMUM OF 2.5 DC MICRO AMPS
(2.5 µA) TO PROVE FLAME AT BURNER
Servicing should only be performed by a Qualied Service Agent
WOVEN STEEL
FIBER SURFACE
Figure 5
11
VENTURI & GAS TRAIN
The gas train includes a Venturi connected to the inlet of the Combustion Blower. The outlet of the 120 Volt
Gas Valve is also connected to the Venturi by a manifold gas line. There is a shutoff valve installed in the
manifold gas line for start up and service procedures. The Venturi contains a convergent/divergent nozzle
(cone shaped restrictor) that constricts the air passage to the blower. As air enters the constriction point its
velocity increases. A pressure drop occurs at this point and creates a negative (vacuum) pressure in the
cavity between the nozzle and the Venturi housing. This negative pressure “pulls” gas from the outlet of the
120 Volt Gas Valve into the blower where it is mixed with combustion air and then supplied to the burner, see
Figure 6.
As the Combustion Blower speed is increased (page 10) the velocity of air owing through the Venturi is also
increased. This increases the vacuum created by the Venturi and more fuel gas is pulled from the 120 Volt
Gas Valve and supplied to the Burner. This increases the ring rate (input Btu/hr) of the VF Boiler. As the
blower speed is decreased less fuel gas is supplied to the Burner and the ring rate is reduced.
The MCB controls blower speed according to system temperature. When system temperature sensed at the
Controlling Probe (page 7) is well below the Operating Set Point the MCB will run the blower at maximum
speed = 100% ring rate. As system temperature rises closer to the Operating Set Point the MCB will reduce
blower speed which reduces (modulates) the ring rate. VF Boilers are designed to modulate between 25%
and 100%; a 4 to 1 turn down rate.
VENTURI OPERATION
COMBUSTION
BLOWER
VENTURI
Negative Pressure
Velocity Increases
At Constriction Point.
Pressure Drops
Negative Pressure
COMBUSTION
AIR INTAKE
NOZZLE
COMBUSTION
BLOWER
BURNER
GAS TRAIN TOP VIEW
VENTURI
MANIFOLD
GAS LINE
120 VAC
GAS VALVE
MANIFOLD GAS
FUEL GAS
120 VAC
GAS VALVE
COMBUSTION
AIR INTAKE
MANIFOLD PRESSURE
SENSING PORT
MANIFOLD GAS
SHUTOFF VALVE
SUPPLY GAS TEST
PORT 1/8” NPT
SUPPLY
GAS
SUPPLY GAS
SHUTOFF VALVE
12
Figure 6
Servicing should only be performed by a Qualied Service Agent
CONFIG KEY
The Cong Key is an 18” long cable with a plug on one end and an EEPROM memory chip sealed at the
other. The Cong Key plugs into the J23 socket on the MCB, see MCB - Section H on page 27. The memory
chip contains blower speed programming data specic to the input Btu/hr and fuel type for each VF Boiler.
VF Boilers are available in natural and propane gas and in ve input Btu/hr models ranging from 500,000 to
2,000,000. This Service Manual covers the 1,500,000 and 2,000,000 Btu/hr models only.
Each time the Boiler is powered up the MCB reads and then stores the blower speed programming data
from the Cong Key into it’s own internal memory. The MCB then uses the data to modulate the Combustion
Blower speed by sending instructions from the MCB J24 socket to the 5 pin socket on the Combustion Blower
Assembly, see Figure 4 on page 10 and MCB - Section H on page 27. Modulating the Combustion Blower speed
also modulates the ring rate on VF Boilers, see Venturi & Gas Train on page 12.
There is a label at the end of the Cong Key cable near the memory chip that identies which boiler model it is
used for. This end of the cable is threaded into the wiring chase during manufacturing. The software revision
for the Cong Key can be viewed in the Log & System Info menu, see Control System Menus on page 44.
WARNING:
Cong Keys are manufactured for a particular fuel type and input Btu/hr rating as described above. Cong
Keys MUST NOT be interchanged in the eld for any reason. Doing so can cause ignition failure, rough
starting/operation and poor combustion. Changing a Cong Key can permanently damage the Boiler, cause
property damage, personal injury or death. Damage to the Boiler caused by interchanging Cong Keys in the
eld is not covered under the limited warranty as this would be considered a eld alteration of the Boiler's
design.
If it is suspected the Cong Key is defective or the Boiler is experiencing ignition failure, rough starting/
operation and/or poor combustion, ensure the proper Cong Key is installed. Navigate to the Log & System
Info menu in the control system and record the kBTU Rating, Fuel Type and Cong Key Rev number, see
Control System Navigation on page 40 and Control System Menus on page 44. If the Fuel Type and/or kBTU
rating listed in the Log & System Info menu does not match the rating plate on the Boiler, turn the Boiler off
and disable Boiler operation. Call the toll free support phone number on the back cover of this manual for
further assistance.
Figure 7
Servicing should only be performed by a Qualied Service Agent
13
COMBUSTION BLOWER SPEED DATA
Nominal Combustion Blower speeds during various operating states for natural gas models are shown in
Table 1 below. Combustion Blower speeds for propane models are shown in Table 2. Due to slip in the
Combustion Blower and manufacturing tolerances in the electronic speed control these numbers will vary.
When combustion is poor, the ring rate of the Boiler or the Combustion Blower speed is in question, or the
Boiler is experiencing rough starting/operation or ignition failure compare the values given here to actual
blower speeds shown in the Control States menu. The current blower speed (RPM) and operating state can
be viewed in real time in the Control States menu, see Control System Navigation on page 40 and Control
System Menus on page 44.
Viewing the Combustion Blower speed data can also be useful if the Cong Key (see page 13) is suspected as
being defective. Actual blower speeds will vary somewhat but should be relatively close to what is shown in
the tables below. If Combustion Blower speeds vary greatly, 25% or more, or if the Cong Key is suspected
as being defective call the toll free support phone number on the back cover of this manual for further
assistance.
TABLE 1
NATURAL GAS MODELS
OPERATING STATE VW/VB 1500
NOMINAL BLOWER SPEED
Pre/Post Purge Periods 4950 RPM 4950 RPM
Ignition Trial Period 1800 RPM 1800 RPM
Forced Maximum Firing Rate 100% 3700 RPM 4650 RPM
Forced Minimum Firing Rate 25% 920 RPM 1225 RPM
NOMINAL BLOWER SPEED
VW/VB 2000
TABLE 2
PROPANE GAS MODELS
OPERATING STATE VW/VB 1500
NOMINAL BLOWER SPEED
Pre/Post Purge Periods 4950 RPM 4950 RPM
Ignition Trial Period 1800 RPM 1800 RPM
Forced Maximum Firing Rate 100% 3700 RPM 4415 RPM
Forced Minimum Firing Rate 25% 900 RPM 1170 RPM
NOMINAL BLOWER SPEED
VW/VB 2000
14
Servicing should only be performed by a Qualied Service Agent
TEMPERATURE PROBES
Temperature probes are 3/4 inch male NPT threaded immersion probes, see Figure 8. Temperature probes
have embedded temperature sensors (thermistors). Thermistors are thermally sensitive resistors; as the
surrounding temperature rises the resistance of the thermistor (measured in ohms) will decrease and as the
surrounding temperature falls the resistance of the thermistor increases, see Table 3 on page 16. The Boiler’s
Control System monitors these sensors to determine water temperature at various points in the system.
INLET / REMOTE TEMPERATURE PROBE
OUTLET TEMPERATURE PROBE
Figure 8
INLET AND OUTLET TEMPERATURE PROBES
All VF Boilers have one Inlet and one Outlet Temperature Probe factory installed in the top of the Heat
Exchanger to monitor the water temperature entering and leaving the Boiler. The Inlet Probe is a temperature
sensor only and has two wiring leads. The Outlet probe also contains the manual reset high temperature
limit switch and has four wiring leads. The Control System displays the Inlet and Outlet water temperatures
sensed from these two probes on the default Temperatures Menu. The Control System also displays the
temperature difference between the Inlet and Outlet Temperature Probes on the Temperatures Menu as the
"Delta T" value. See Figure 29 on page 40.
REMOTE TEMPERATURE PROBE
All VF Boilers are supplied from the factory with a Remote Temperature Probe. The supplied Remote
Temperature Probe is used to control system water temperature for a single boiler in a domestic hot water
storage tank or in the return line from a primary/secondary hydronic heating system. Use of the Remote
Temperature Probe allows a boiler to sense the actual water temperature inside the storage tank or hydronic
heating loop. The Boiler will modulate its ring rate in response to the actual system temperature and load
conditions. The Control System displays the temperature sensed from the Remote Temperature Probe as the
“Tank” temperature on the default Temperatures Menu. See Figure 29 on page 40.
QUAD THERMISTOR PROBE
When connecting up to 4 boilers to a single storage tank or one primary/secondary hydronic heating system
the optional Quad Thermistor Probe should be used. The Quad Thermistor Probe is a remote temperature
probe with four temperature sensors embedded in one device. The Quad Thermistor Probe allows up to 4
boilers to sense system temperature from the same point in the system. Use of the Quad Thermistor Probe
will allow each connected boiler to individually sense the actual water temperature in the storage tank or the
hydronic heating loop. The temperatures sensed from each of the four temperature sensor circuits in a Quad
Thermistor Probe are shown as the “Tank” temperature on each Boiler’s default Temperatures Menu. See
Figure 29 on page 40.
Servicing should only be performed by a Qualied Service Agent
15
QUAD THERMISTOR PROBE
FOUR (2 WIRE - COLOR CODED)
TEMPERATURE SENSOR CIRCUITS
FOR USE WITH MULTIPLE BOILERS.
FACTORY EQUIPPED WITH 6 x 1/2 INCH NPT PIPE NIPPLE
TO ACCOMMODATE STORAGE TANK INSULATION THICKNESS.
THIS CAN BE FIELD REPLACED WITH A SHORTER NIPPLE
TO ACCOMMODATE VARIOUS TANKS AND HEATING LOOPS.
EIGHT WIRE TERMINAL
STRIP FOR CONNECTIONS
MOUNTED INSIDE THE
PROBE COVER
SIDE VIEW
REMOVE 1/8 INCH ALLEN SET SCREW
IN PROBE END TO REPLACE FACTORY
NIPPLE WITH FIELD SUPPLIED NIPPLE.
Figure 9
OPERATIONAL NOTES: When using multiple boilers with the Quad Thermistor Probe staggering each
Boiler's Operating Setpoint by 1° to 3° will achieve greater system energy savings. The Boiler(s) with the
lower Operating Setpoint will reduce their ring rate rst and cycle off before the boiler(s) with higher settings.
Setting up a monthly maintenance schedule to rotate which boiler(s) has the higher Operating Setpoint will
also provide a means for lead/lag control which will maintain even wear/operating time for each boiler.
TABLE 3
WATER TEMPERATURE TEMPERATURE SENSOR
RESISTANCE IN OHMS
16
CELSIUS FAHRENHEIT
3° 40° 26,435
21° 70° 11,974
38° 100° 5,862
49° 120° 3,780
55° 130° 3,066
60° 140° 2,503
71° 160° 1,698
82° 180° 1,177
Servicing should only be performed by a Qualied Service Agent
CONTROL PANEL
Figure 10 shows the Control Panel layout inside the VF Boiler. Three pressure switches are located in
the upper right corner. Directly beneath the pressure switches is the Pump Relay that energizes factory
installed Boiler Circulation Pumps or eld supplied 120 VAC pumps up to 1 horsepower. For higher voltage/
horsepower pumps a eld supplied starter must be used. The black and white 120 VAC pump wiring in the
junction box on the back of the Boiler would be used to power the eld supplied starter coil in this case. The
MCB (Modulation Control Board) and the PDB (Power Distribution Board are also located on the Control
Panel. The optional LWCO (Low Water Cut Off) circuit board is mounted on the Control Panel on models so
equipped.
PRESSURE SWITCHES
BLOCKED FLUE
(EXHAUST)
BLOCKED
INTAKE AIR
BLOWER
PROVER
MCB
(Modulation Control Board)
BOILER
CIRCULATION
PUMP RELAY
(Power Distribution Board)
LWCO CIRCUIT BOARD
(Low Water Cut Off)
PDB
ON/OFF
POWER RELAY
Figure 10
Servicing should only be performed by a Qualied Service Agent
17
PRESSURE SWITCHES
Blocked Flue (Exhaust) Switch
Normally Closed, Opens On Pressure Rise
Natural Gas
Propane Gas
Single Pressure Sensing
Blocked Intake Air Switch
Normally Closed, Opens On Pressure Fall
Single Pressure Sensing
-4.0" W.C. ± 0.18
-5.7" W.C. ± 0.18
Blower Prover Switch
Normally Open, Closes On Differential
Natural Gas
Propane Gas
There are three pressure switches installed on all VF Boilers to verify the venting (exhaust) and the intake air
are not restricted and to conrm the Combustion Blower is operating properly when energized, see Figure 10
on page 17 and Figure 11 below.
The sensing tubes must be routed to the correct sensing ports and they must be properly connected at all
times. Improper routing, kinks and disconnected sensing tubes will cause improper operation and associated
Control System lock outs. The Blower Prover switch is a dual pressure switch, when testing performance
two pressure readings are necessary. If the two sensing tubes connected to the Blower Prover switch are
reversed, the Control System will lock out and display the "Blower Prover" error message on the LCD.
Figure 11 below illustrates the proper routing for the pressure switches and provides the operating parameters
for each switch. Refer to this illustration when testing pressure switch performance or verifying proper sensing
tube routing.
PRESSURE SWITCHES
OPERATIONAL
PARAMETERS
+3.5" W.C. ± 0.18 +4.0" W.C. ± 0.18
Natural Gas Propane Gas
Dual Pressure Sensing
-4.0" W.C. ± 0.18 -4.0" W.C. ± 0.18
WIRING
TERMINALS
TO ALUMINUM
CONNECTING
TUBE FROM
COMBUSTION
CHAMBER
BLOCKED FLUE
(EXHAUST)
PRESSURE SWITCH
SENSING TUBES
BLOCKED
INTAKE AIR
TO INTAKE AIR
SENSING PORT
BLOWER
PROVER
P1P1 P2P2
B
TO MANIFOLD PRESSURE
A
SENSING PORT
18
Servicing should only be performed by a Qualied Service Agent
INTAKE AIR
SENSING PORT
MANIFOLD
PRESSURE
SENSING PORT
B
Figure 11
A
MCB - MODULATION CONTROL BOARD
The MCB circuit board is the main controller and is located on the Control Panel, see Figure 10 on page 17. All
instructions for Burner modulation and temperature control originate from this circuit board. Diagnostic and
operational messages are generated by the MCB and sent to the UIM. Most of the Boiler’s components, such
as the Igniter, Combustion Blower, 120 VAC Gas Valve, and Temperature Probes are directly connected to
one of the MCB’s socket connectors. The UIM (User Interface Module, see page 40) is also connected to one
of the internal communication ports on the MCB. The Flame Sensors (see Figure 5 on page 11) are connected
to the J16 spade connector on the MCB. Optional iCOMM™ system hardware, when used, is connected to
one of the external communication ports on the MCB. The MCB circuit board has been divided into sections
in the illustration below, each section will be covered in the pages that follow.
DE
J7J8
J6
F
G
J9
ICSP
EXT
COMM
EXT
COMM
INT
COMM
INT
COMM
SW2
SW1
J23
J24
H
MCB
(Modulation Control Board)
RED LED
F1 FUSE
J3
J4
J11
J5
J17
J19
A
B
J2
J15
J1
J16
Figure 12
Servicing should only be performed by a Qualied Service Agent
J18
C
19
MCB - SECTION A
See Figure 12 on page 19 for location of this section on the MCB.
RED LED
F1 FUSE
A
J3
1 2 3
Figure 13
The upper right corner of the MCB contains the following sockets/components:
• Red LED (illuminated when the F1 fuse is open or not installed)
• F1 Fuse (7.5 amp automotive fuse - transformer secondary [24 VAC] winding protection)
• J3 Socket (24 VAC power supply from transformer)
• Pin 1 - 24 VAC from PDB J2 Socket Pin 1
• Pin 2 - 24 VAC from PDB J2 Socket Pin 2
• Pin 3 - Ground from PDB J2 Socket Pin 3
20
Servicing should only be performed by a Qualied Service Agent
MCB - SECTION B
See Figure 12 on page 19 for location of this section on the MCB.
5
4 3
2 1
J4
10
9 8 7 6
J11
1 2
3
10
9 8 7 6
J5
J17
J19
• J4 Socket (Outputs/Inputs)
• Pin 1 - Power Accessory 24 VAC
• Pin 2 - Power Accessory Prover
• Pin 3 - Power Accessory 24 VAC RTN
• Pin 4 - 24 VAC line low water cut off (optional)
• Pin 5 - Low water cut off proving signal
• Pin 6 - 24 VAC line low water cut off (optional)
• † Pin 7 - 24 VAC alarm bell circuit (optional)
• † Pin 8 - 24 VAC alarm bell circuit (optional)
• Pin 9 - Spare - not used
• Pin 10 - Spare - not used
• J11 Socket (Enable/Disable Circuit)
• ‡ Pin 1 - 24 VAC to dry control contacts
• ‡ Pin 2 - 24 VAC to dry control contacts
• Pin 3 - Spare - not used
• J19 Socket
• Pin 1 - 120 VAC - Gas Valve solenoid
• Pin 2 - 120 VAC - Gas Valve solenoid
5
4 3 2 1
4
5
6
1 2
Figure 14
B
1
2
3
• J5 Socket (Inputs)
• Pin 1 - 24 VAC Flow Switch
• Pin 2 - 24 VAC Flow Switch
• Pin 3 - 24 VAC Low Gas Pressure Switch
• Pin 4 - 24 VAC Low Gas Pressure Switch
• Pin 5 - 24 VAC Blocked Flue (Exhaust) Switch
• Pin 6 - 24 VAC Blocked Flue (Exhaust) Switch
• Pin 7 - Spare - Not used
• Pin 8 - Spare - Not used
• Pin 9 - Spare - Not used
• Pin 10 - Spare - Not used
• J17 Socket (Blower Prover/Hi Gas Press Switch)
• Pin 1 - 24 VAC Blower Prover Switch
• Pin 2 - 24 VAC Blower Prover Switch
• Pin 3 - 24 VAC High gas press switch (optional)
• Pin 4 - 24 VAC High gas press switch (optional)
• Pin 5 - 24 VAC Blocked Intake Air Switch
• Pin 6 - 24 VAC Blocked Intake Air Switch
† J4 Socket Pins 7 & 8 provide 24 VAC for an optional alarm bell that will sound whenever the Boiler Control
System declares a fault condition. This is a switched 24 VAC control circuit with a maximum amp rating of 1
AC amp @ 24 VAC.
‡ The enable/disable circuit is provided for use with external supervisory controls. Field wring is installed
between this circuit and a set of "dry contacts" on the external control, see Figure 1 on page 6. This is a
switching circuit only: Do not apply any external voltage or connect any load (IE: relay coil) to this circuit. This
will permanently damage the MCB circuit board and is not covered under the limited warranty.
Servicing should only be performed by a Qualied Service Agent
21
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