State Water Heaters GP650 HTPDT How to use

1
PRINTED 0308 198148-000
COMMERCIAL / RESIDENTIAL GAS WATER HEATERS
FOR MODELS:
 • SHE50-100NE
 • SHE50-100PE
 • GP650YTPDT
 • GP650HTPDT
SERVICE HANDBOOK
ULTRAHIGHEFFICIENCY
POWERVENT/POWERDIRECTVENT

ULTRA HIGH EFFICIENCY
POWER VENT/POWER DIRECT VENT
SERVICE MANUAL
Technical Literature Department ©2008
TABLE OF CONTENTS
INTRODUCTION ............................................................ 2
Qualifications............................................................ 2
Service Warning ....................................................... 2
Important Service Reminder..................................... 2
Instruction Manual .................................................... 3
Tools Required.......................................................... 3
INSTALLATION CONSIDERATIONS............................. 4
Closed Water Systems............................................. 4
Thermal Expansion................................................... 4
Air Requirements...................................................... 5
Contaminated Air...................................................... 5
Venting...................................................................... 6
Electrical Requirements............................................ 8
OPERATION & SERVICE............................................... 9
How it works............................................................. 9
Blower..................................................................... 10
Burner......................................................................11
Venturi .................................................................... 14
Gas Valve ............................................................... 15
Gas Pressure Testing............................................. 16
Air Pressure Switches ............................................ 18
Air Pressure Switch Operation ............................... 20
Air Pressure Switch Testing.................................... 21
Flame Sensing Test................................................ 24
Igniter Current Test................................................. 25
CONTROL SYSTEM..................................................... 26
Introduction............................................................. 26
UIM......................................................................... 27
Discreet Menu - Contact Information ............... 28
Operating Set Point Adjustment............................. 32
Control System Menus........................................... 33
CCB........................................................................ 35
Socket Identification......................................... 36
Wiring Diagram....................................................... 39
Sequence of Operation........................................... 40
TROUBLESHOOTING...................................................41
Rough Start - Rough Operation............13 and 41
Heater Status Menu..........................................33
Things to Check Before Servicing ....................41
Reset Procedure...............................................41
Control System Unresponsive.................................42
Blank Display....................................................42
UIM Inoperable.................................................42
Fault Messages.......................................................43
AC Reversed ....................................................43
Upper Probe Open............................................43
Upper Probe Short............................................44
Flame Probe Short............................................44
Flame Detect Error ...........................................45
Energy Cut Out (ECO)......................................45
Blocked Inlet.....................................................46
Blocked Exhaust Vent.......................................47
Blower Prover Failure.......................................47
Blower Prover Open - Blower Not Running ......48
Blower Prover Open - Blower Is Running.........48
Low Igniter Current...........................................49
Ignition Failure..................................................50
Gas Valve Failure .............................................52
Communication Failure.....................................52

ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
Technical Literature Department 2 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
INTRODUCTION
This Service Manual is designed to be an aid in servicing and troubleshooting the 96%
thermally efficient, 50 gallon, 100,000 Btu/hr residential and light duty commercial power
vent - power direct vent model water heaters listed on the cover of this manual.The
instructions, illustrations and procedures contained in this manual are used to verify proper
operation and to diagnose and repair common service problems.
This manual does not replace or supersede the Instruction Manual that came with the water
heater. Always refer to the Instruction Manual that came with the water heater for complete
installation instructions. If the Instruction Manual is not available copies can be obtained
from the manufacturers web site or by calling the technical support phone number shown on
the water heater labeling.
QUALIFICATIONS - QUALIFIED SERVICE AGENT
Servicing the products referenced in this manual requires the ability (in the field involved)
equivalent to that of a Qualified Service Agent as defined by the American National
Standards Institute (ANSI) below. Installation skills such as plumbing, air supply, venting,
gas supply, electrical supply are required in addition to diagnostic and electrical testing
skills.
ANSI Z223.1 2006 Sec. 3.3.83: “Qualified Agency” - “Any individual, firm, 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 qualified (as defined by ANSI above) and licensed or certified as required by
the authority having jurisdiction to perform a given task do not attempt to perform any of the
service or installation procedures described in this manual. If you do not understand the
instructions given in this manual or do not feel confident in your abilities to perform a given
task do not attempt to perform any procedures outlined in this manual.
IMPORTANT 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 replacement. 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.

Technical Literature Department 3 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
INSTRUCTION MANUAL
Have a copy of the Instruction Manual that came with the water heater on hand for the
correct model water heater you are working with before servicing.
Installation information given in this Service Manual is not a complete installation
instruction. Installation information covered in this Service Manual has a limited focus as it
applies to servicing. This Service Manual does not replace or supersede the Instruction
Manual that came with the water heater. Always refer to the Instruction Manual that came
with the water heater 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 technical support phone number shown on the water heater labeling.
TOOLS REQUIRED
• Instruction Manual that came with the water heater.
• All tools common to installation and service of commercial water heaters such as hand
tools, torch, pipe wrenches etc.
• Long (8-10”) T handle SAE hex (allen key) wrenches including 5/32”, 1/8” and 1/4” - for
blower, burner, and gas valve removal and installation.
• Two digital manometers range -20.00 to +20.00" W.C., resolution - 0.01" W.C.
Recommend UEI model EM200 or equivalent. Required to test performance of air
pressure switches. Also used to measure low pressure supply gas and manifold gas
pressure.
• Digital Multi Meter DMM; recommend Fieldpiece HS36, Fluke 187, UEI DL289 or
equivalent capable of measuring:
• AC/DC Voltage
• AC Frequency (Hz)
•Ohms
• DC micro amps µA (flame sensing current)
• AC amp meter- recommend UEI model DL289 or equivalent.
• 120 VAC household outlet tester (see Service Notes Electrical page 8)

ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
Technical Literature Department 4 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
INSTALLATION CONSIDERATIONS
INSTRUCTION MANUAL
Installation information given in this Service Manual is not a complete installation
instruction. Installation information covered in this Service Manual has a limited focus as it
applies to servicing. This Service Manual does not replace or supersede the Instruction
Manual that came with the water heater. Always refer to the Instruction Manual that came
with the water heater for complete installation instructions.
If the instruction Manual that came with the water heater is not on hand copies can be
obtained from the manufacturers web site or by calling the technical support phone number
shown on the water heater labeling.
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 flow preventers. Devices such as these cause the water system to be a
closed system.
Virtually all commercial and most residential water supply systems are closed systems
today. Closed water systems will experience thermal expansion which, if not controlled with
a properly installed and sized thermal expansion tank, can cause premature failure
(leakage) of the water heater. Water heater failure (leakage) on closed systems where there
is not a thermal expansion tank installed is not covered under the limited warranty.
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 should be installed on all closed systems to control
the harmful effects of thermal expansion.

Technical Literature Department 5 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
AIR REQUIREMENTS
Carefully review the requirements for combustion and ventilation air in the Instruction
Manual that came with the water heater. Failure to meet these requirements when the water
heater is installed or overlooking their importance when servicing the water heater often
results in needless down time, unnecessary parts replacement, and customer
dissatisfaction. If the Instruction Manual is not on hand copies can be obtained from the
manufacturers web site or by calling the technical support phone number shown on the
water heater labeling.
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 air pressure switches.
CONTAMINATED AIR
Combustion air that is contaminated can greatly diminish the life span of the water heater
and water heater components such as hot surface 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 flammable in many cases, can also react to form
highly corrosive substances such as hydrochloric acid inside the water heater’s combustion
chamber. The results can be hazardous and cause product failure.
If this water heater will be installed in beauty shops, barber shops or laundries with dry
cleaning equipment, it is imperative the water heater be installed as a Direct Vent appliance
so that air for combustion is derived directly from the outside atmosphere through a sealed
intake air pipe. See the Installation of Vent System section in the Instruction Manual that
came with the water heater for more information on Direct Vent installations.

ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
Technical Literature Department 6 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
VENTING
The venting information presented in this Service Manual is not a complete venting
installation instruction. Refer to the Instruction Manual that came with the water heater for
complete installation instructions.
The water heater covered in this Service Manual may be installed as a conventionally
vented water heater or as a direct vent water heater. Conventional vent installations use
room air for combustion. There will be one “vent” pipe installed on a conventional vent
installation. Direct vent installations derive all air for combustion from the outdoor
atmosphere through a second “intake air” pipe. There will be two pipes (vent and intake air)
installed on a direct vent installation.
The vent and intake air piping (direct vent installations) may not be combined with any other
appliances under any conditions.
Maximum Equivalent Length Requirements
The vent and intake air pipe (direct vent installations) for the water heater covered in this
Service Manual can be installed using 2, 3, or 4 inch pipe depending on the overall
“equivalent” length of each pipe; see Table 1 on page 7.
The vent and intake air terminations do not factor into the overall equivalent feet
calculations.
The vent and intake air connection fittings on the water heater do not factor into the overall
equivalent feet calculations.
Additional 2 or 3 inch 90° elbows installed are equivalent to 5 linear feet of pipe. Additional 4
inch 90° elbows are equivalent to 8 linear feet of pipe. 45° elbows will count for half the
equivalent length a 90° elbow does.
Overall equivalent lengths are determined by adding the total length of pipe installed to the
accumulated total equivalent length of all the additional elbows factored in.
The maximum equivalent lengths given in the Instruction Manual that came with the water
heater and shown in Table 1 (page 7) are for the vent pipe AND for the intake air pipe. IE: A
2 inch vent pipe can be up to 20 equivalent feet with one 90° elbow. On a direct vent
installation the 2 inch intake air pipe can also be up to 20 equivalent feet with one 90° elbow.
Carefully review the venting installation instructions and maximum equivalent length
requirements for the vent and intake air piping. Ensure the vent system has been installed
per Instruction Manual requirements.
2”
3”
4”
= 5 linear feet of pipe
= 5 linear feet of pipe
= 8 linear feet of pipe

Technical Literature Department 7 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
VENTING (CONT)
Pipe Size Requirements
Ensure the correct size pipe has been used for the overall equivalent length of the vent and
intake air piping installed. Longer equivalent lengths require larger pipe sizes, see Table 1.
Maximum Elbow Requirements
Three and four inch vent and intake air pipe installations allow a maximum of 6 - 90° elbows
in the vent pipe AND a maximum 6 - 90°elbows in the intake air pipe. Two inch installations
allow a maximum of 3 - 90° elbows in the vent pipe AND a maximum 3 - 90° elbows the
intake air pipe.
Table 1
Service Notes - Venting
Remove all plastic debris from the edges of intake air pipe sections after cutting on direct
vent installations. Plastic debris left on intake air pipe sections can collect inside and clog the
burner and lead to rough operation and/or ignition failure. See Service Notes page 11.
Using a smaller pipe size than required for a given length or installing more elbows on the
vent pipe can cause the water heater’s control system to declare a fault condition, lock out
and display the “Blocked Exhaust” fault message on the UIM display (see page 27).
Overlooking the same requirements for the intake air pipe on direct vent installations or
failing to remove the screen from the intake air connection when direct venting can cause
the water heater’s control system to declare a fault condition, lock out and display the
“Blocked Inlet” fault message on the UIM display (see page 27).
NUMBER
90° ELBOWS
2” MAXIMUM PIPE
LENGTH FEET (METERS)
3” MAXIMUM PIPE
LENGTH FEET (METERS)
4” MAXIMUM PIPE
LENGTH FEET (METERS)
1 20 (6.1) 60 (18.3) 120 (36.6)
2 15 (4.6) 55 (16.8) 112 (34.1)
3 10 (3.0) 50 (15.2) 104 (31.7)
44 elbows not allowed in 2” pipe
(use larger pipe size) 45 (13.7) 96 (29.3)
55 elbows not allowed in 2” pipe
(use larger pipe size) 40 (12.2) 88 (26.8)
66 elbows not allowed in 2” pipe
(use larger pipe size) 35 (10.7) 80 (24.3)
The screen inside the intake air connection is meant to keep
larger debris from entering the blower when the water heater is
installed conventionally; using room air for combustion.
When the water heater is installed in a direct vent configuration
the screen inside the intake air connection on the water heater
must be removed. If left in place it will become clogged over time
and lead to “Blocked Inlet” lock out conditions.
The screen on the intake air termination will keep larger debris
from entering the blower on direct vent installations.
Remove This Screen
For Direct Vent
Installations

ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
Technical Literature Department 8 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
ELECTRICAL REQUIREMENTS
The water heater covered by this Service Manual must be grounded in accordance with
the local codes, or in the absence of local codes: the National Electrical Code (NFPA 70) or
the Canadian Electrical Code (C22.1).
The water heater covered by this Service Manual requires a 120 VAC 1Ø (single phase)
power supply. It is factory equipped with a standard 3 prong appliance cord that plugs into a
standard 120 VAC wall outlet. 5.2 FLA (full load amps) approximate.
As shown in the illustration below there should be 120 VAC present between the power
supply hot and ground wires. 120 VAC should also present between the hot and neutral
wires. There should be 0 VAC present between the neutral and ground wires.
Correct wiring for a standard 120 VAC wall outlet is also shown in the Illustration below. Note
the orientation of the ground connect is at the bottom. Reversed polarity is when the hot and
neutral wires are connected opposite from what is shown here.
Service Notes - Electrical
This water heater is a polarity sensitive appliance and will not operate if the power supply
polarity is reversed. If the polarity of the power supply is reversed the water heater’s control
system will declare a fault condition and display “AC Reversed” on the UIM display.
The water heater’s burner must be grounded for flame sensing current to be established and
verify ignition. If the burner is not grounded the water heater’s control system will declare a
fault condition and display “Ignition Failure” on the UIM display after 3 failed ignition trials.
Also shown is an outlet tester that will quickly determine if the plug is wired correctly. These
testers will also diagnose reversed polarity, open ground and open neutral wire problems.
Outlet testers are inexpensive and simple to use. They are available at most hardware
stores and home centers.
120 volts
120 volts
0 volts
HOT NEUTRAL GROUND
HotNeutral
Ground
120 VAC 1Ø
Wall Outlet
Correctly Wired Outlet120 VAC 1Ø Power Supply
Outlet Tester

Technical Literature Department 9 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
OPERATION & SERVICE
HOW IT WORKS
This section of the Service Manual will cover operation, common service procedures and
water heater construction. The water heater covered in this Service Manual has a helical coil
shaped heat exchanger that is submerged in the storage tank. The water heater uses a top
mounted down fired radial burner. This is a forced draft burner; hot burning gases are forced
through the heat exchanger under pressure and exit through the exhaust/vent connection
located at the bottom of the water heater.
COMBUSTION
AIR INTAKE
CONNECTION
EXHAUST/VENT
CONNECTION
INTERNAL VIEW
EXTERNAL VIEW
Starting at the top combustion air and
fuel gas are drawn in by the blower
(page 10) and Venturi (page 14).
The hot burning gases exit the radial
burner (page 11) and are forced
through the coil shaped heat
exchanger.
Flue gases spiral through the heat
exchanger and exit the water heater
through the exhaust/vent connection
at the bottom.
HELICAL
SHAPED
HEAT EXHNGER
BLOWER/BURNER
GAS VALVE
ASSEMBLY
COMBUSTION
AIR INTAKE
CONNECTION
EXHAUST/VENT
CONNECTION

ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
Technical Literature Department 10 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
BLOWER
The blower is an assembly consisting of the blower housing, motor and an integrated VFD
(variable frequency drive). Blower operation is controlled by the CCB (central control
board - page 35). The CCB sends 120 VAC to the Blower/VFD assembly high voltage 3 pin
socket. The CCB also sends a PWM (pulse width modulation) signal to the Blower/VFD
assembly low voltage 5 pin socket.
The PWM signal is a digital instruction sent to the VFD instructing it to start, stop, and control
blower speed. The VFD powers the blower motor directly. The VFD also varies the
frequency (Hz) of the power it sends to the blower motor which in turn controls blower
speed. Higher frequency = faster blower speed, lower frequency = slower blower speed.
Service Notes - Blower
The PWM signal plug MUST remain plugged in to the 5 pin socket on the blower assembly
at all times. Removing this plug will cause the blower to accelerate and the Btu/hr input of
the water heater to increase to a much higher rate. This may cause damage to the water
heater.
Blower Motor / VFD Assembly
Blower Housing
High Voltage 120 VAC 3 Pin Socket
Low Voltage PWM 5 Pin Socket

Technical Literature Department 11 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
BURNER
The images below show a complete blower/burner assembly removed along with a top view
of the water heater with the blower removed.
Service Notes - Burner (Flame Sensor)
The burner installed in the water heater is a radial fire burner. Radial fire burners can trap
debris that enter the blower. Be sure to thoroughly clean the edges of intake air pipe
sections after cutting during the installation. If this is not done plastic shavings can collect
inside the burner and lead to rough operation and/or ignition failure.
The burner should be removed and inspected whenever servicing for rough operation or
ignition failure problems. Burner removal requires removal of the blower. Blower removal
requires 8-10” long T handle 1/8” hex (allen) wrench.
The flame sensor will accumulate corrosion (rust etc) over time. This will reduce flame
sensing current. This is the most common cause of “Ignition Failure” lock outs. The flame
sensor should cleaned when servicing due to ignition failure and as a routine maintenance
procedure. Fine grade steel wool is recommended for cleaning the flame sensor; do not use
coarse abrasives such as sand paper.
Radial Fire Burner
Igniter
Blower VFD Flame Sensor
Top View Water Heater - Blower Removed
Blower removal
requires 8 -10” long T
handle 1/8” hex (allen)
wrench.
Burner must be grounded
for flame sensing current to
beestablished.SeeService
Notes - Electrical page 8
Burner Ground Wire Blower Adapter
Assembly
Burner View Port
Blower Adapter

ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
Technical Literature Department 12 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
BURNER (CONT)
Burner & Blower Removal
The burner should be removed and inspected whenever service is being performed for
rough operation or ignition failure. Radial fire burners like the one used on this water heater
can trap debris, see Service Notes - Venting on page 7.
The following images illustrate the burner removal procedure. Long T handle hex wrenches
(8-10”) will save considerable time when removing/installing the burner & blower.
BLOWER/BURNER REMOVAL PROCEDURE
1 Ensure power to the water heater is turned off.
2 The blower assembly must be removed first.
3 Disconnect the two wiring plugs from the blower
assembly sockets (see Service Notes - Blower
page 10).
4 Disconnect the Blower Prover air pressure switch
sensing tube.
5 Remove 4 blower flange mounting screws -
1/8” hex. Using long T handle hex wrench will
save considerable time.Do not over tighten when
reinstalling - torque should not exceed 40 inch
lbs.
6 Remove the blower assembly from the blower
adapter.
7 Remove the blower flange gasket. Gasket may be
reused if not damaged or showing signs of
excessive wear.
8 Remove the flame sensor - 1 Phillips head screw.
CONTINUED ON NEXT PAGE
Blower Flange
Blower Adapter
1/8” Hex Machine Screws Blower Flange
Blower Flange Gasket
Flame Sensor
Blower Prover Sensing Tube

Technical Literature Department 13 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
BURNER (CONT)
Burner/Blower Removal (cont)
Service Notes - Blower Flange & Blower Adapter Gaskets.
Whenever the blower or burner is removed for service DO NOT overtighten the machine
screws that hold the blower flange to the blower adapter (page 12) or the blower adapter to
the water heater tank (above). Torque on these screws should not exceed 40 inch lbs.
If these mounting screws are overtightened the gaskets will be squeezed and deformed
from their natural shape. This can partially block the flow of the fuel air mixture and cause
rough starting, rough operation and ignition failure.
If these gaskets are deformed from overtightening the mounting screws it can also lead to
gasket leakage. Hot flue gases leaking from these points can burn up wiring, igniters, and
other components.
Blower Adapter
BLOWER/BURNER REMOVAL PROCEDURE
(CONT)
9 Remove 4 blower adapter 1/4” hex machine
screws. Do not over tighten when reinstalling -
torque should not exceed 40 inch lbs.
10 Remove the blower adapter.
11 Be extremely careful when handling the Sight
Glass inside the Burner View Port (page 11) this
can easily be dropped and lost - and the water
heater must have the sight glass in place to
operate safely.
12 Remove the hot surface igniter - 2 Phillips head
screws.
13 Remove the blower adapter gasket. Gasket may
be reused if not damaged or showing signs of
excessive wear.
14 Lift the burner up and out.
1/4” Hex Machine Screws
Hot Surface Igniter
Burner
Blower Adapter Gasket
Sight Glass inside
Burner View Port

ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
Technical Literature Department 14 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
VENTURI
A Venturi is connected to the inlet of the blower. All combustion air flows through the Venturi.
The outlet of the 24 VAC gas valve connects directly to the side of the Venturi. Fuel gas
flows from the outlet of the gas valve into the side of the Venturi directly.
Inside the Venturi there is a cone shaped restrictor that constricts the air passage to the
blower inlet. As air enters the constriction point it’s velocity increases. A pressure drop
occurs at this point and creates a negative pressure in the cavity between the cone shaped
restrictor and the Venturi housing. This negative pressure “pulls” gas from the outlet of the
gas valve into the blower where it is mixed with combustion air and then supplied to the
burner. See the images below.
GAS
VALVE
Velocity Increases
At Constriction Point
Pressure Drops
Negative Pressure
Negative Pressure
Combustion Air
Venturi Inlet
24 VAC Gas Valve
Gas Inlet
Supply Gas
Blower
Blower
Burner
Venturi

Technical Literature Department 15 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
GAS VALVE
The outlet of the gas valve is connected by flange directly to the side of the Venturi (page
14). There is no manifold gas line on the water heater. A gas orifice with gasket is fitted into
the gas valve’s outlet flange. See the images below.
Gas Valve Removal
The gas valve must be removed to inspect the gas orifice. There are 3 - 5/32” hex head
screws that secure the gas valve to the Venturi. Long T handle hex wrenches (8-10”) will
save considerable time when removing/installing the gas valve, blower and burner.
5/32” hex wrench
Gasket Orifice
Natural Gas Orifice 0.191”
Propane Gas Orifice 0.162”
Venturi
Gas Orifice
& Gasket 24 VAC Gas Valve
Gas Orifice
& Gasket
GAS VALVE REMOVAL PROCEDURE
1 Ensure power to the water heater is turned off.
2 Turn off the supply gas shut off valve.
3 Disconnect supply gas line to water heater.
4 Remove 3 gas valve mounting screws - 5/32” hex
head machine screws. Support gas valve body
when removing last screw. Long T handle hex
wrenches (8-10”) will save considerable time
when removing/installing the gas valve.
5 Carefully lift gas valve body off of flange
connection on Venturi.
6 Gas orifice and gasket are now accessible.
Venturi
24 VAC Gas Valve

ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
Technical Literature Department 16 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
GAS PRESSURE TESTING
The water heater covered in this Service Manual is rated at 100,000 Btu/hr input. It is
certified for elevations up to 10,100 feet (3079 meters) without adjustment. Call the technical
support phone number shown on the water heater labeling before operating the water
heater at higher elevations.
Service Notes - Checking Gas Pressures
Manifold and supply gas pressure can be measured at two test ports on the water heater’s
gas valve. The manifold test port is closest to the blower housing and the supply test port is
furthest. The valve in each test port is opened/closed with a small slotted screwdriver.
Manifold gas pressure will run at 0.00” W.C. or lower, in a negative pressure, depending on
the operating state or mode the control system is currently in (see Venturi on page 14).
Manifold gas pressure will be considerably lower, -6.50” to -7.50” W.C. during the pre/post
purge modes when the blower is running and the gas valve is closed. When the gas valve
opens (energized) gas entering the Venturi will cause a rise in manifold gas pressure.
Manifold gas pressure will vary depending on vent/intake air pipe lengths. Manifold gas
pressure will typically be 0.00” W.C. to +0.05” W.C. during the heating mode.
There may also be a drop in supply gas pressure noticed when the water heater’s gas valve
opens. Seeing a rise in manifold pressure and a corresponding drop in supply gas pressure
confirms the gas valve is opening and gas is flowing to the burner. The procedure for
checking manifold and supply gas pressures is shown in the illustrations that follow.
CHECKING GAS PRESSURES
1 Ensure power to the water heater is turned off.
2 Turn off the supply gas shut off valve.
3 Open the manifold and supply gas pressure test
ports on the gas valve. Turn the needle valve
slotted heads 1/2 to 1 full turn counterclockwise
with a small slotted screwdriver.
4 Attach sensing tube from 2 digital manometers
(see tool requirements page 3) to each gas
pressure test port on the gas valve as shown.
CONTINUED ON NEXT PAGE
Supply Gas
Test Port
Manifold Gas
Test Port
Manifold Gas
Test Port Supply Gas
Test Port
Turn test port needle valves counter-clockwise
to open and clockwise to close. Always close
test ports when finished and check for leaks
Sensing Tubes
From Manometers

Technical Literature Department 17 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
GAS PRESSURES (CONT)
Service Notes - Gas Pressure Adjustment
Manifold gas pressure is factory set and should not be adjusted in the field. If manifold gas
pressure differs greatly from the pressures in Table 2 consider the calibration of the
manometer being used - try a different manometer. Call the technical support phone number
on the water heater label for further assistance if pressures are considerably different.
Table 2 - Gas Pressures
FUEL TYPE †MINIMUM SUPPLY
†. Minimum supply gas pressures must be maintained under both load and no load conditions.
MAXIMUM SUPPLY MANIFOLD
Natural Gas 3.5” W.C. (0.87 kPa) 14.0” W.C. (3.48 kPa) 0.00” to +0.05” W.C.
(0.00 to +0.012 kPa)
Propane Gas 8.0” W.C. (1.99 kPa) 14.0” W.C. (3.48 kPa) 0.00” to +0.05” W.C.
(0.00 to +0.012 kPa)
CHECKING GAS PRESSURES (CONT)
5 Open the supply gas shut off valve - restore
power - start a heating cycle.
6 The rise in manifold pressure and corresponding
drop in supply gas pressure confirms the water
heater’s gas valve is opening and gas is flowing
to the burner.
7 Record the supply and manifold gas pressures
with the water heater firing.
8 Supply gas pressure should not drop below
minimum given in Table 2 below.
9 Manifold gas pressure should be within the range
shown in Table 2 below.
10 Look through the burner view port (page 11)
burner flame should be blue.
11 Shut off power and gas supply - disconnect
manometers - close test port needle valves.
12 Restore power and gas supply. Check for gas
Manifold
Gas Supply Gas
Manifold
Gas Supply Gas Manifold
Gas Supply Gas
1 BLOWER OFF / GAS VALVE OFF
Manifold 0.00” W.C. Supply +9.70” W.C.
2 BLOWER ON / GAS VALVE OFF
Manifold -6.86” W.C. Supply +9.70” W.C. 3 BLOWER ON / GAS VALVE ON Manifold +0.05” W.C. Supply +7.04” W.C.
Typical manifold and supply gas pressures during:
1 Standby Mode
2 Pre-Purge Mode
3 Heating Mode

ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
Technical Literature Department 18 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
AIR PRESSURE SWITCHES
Air pressure switch technical bulletins TB-A023-06 and TB-S023-06 explain air pressure
switch construction and test procedures in detail. These technical bulletins are available on
the manufacturers web site or by calling the technical support phone number shown on the
water heater labeling. Construction and types of air pressure switches used on the water
heater covered in this Service Manual are shown below.
Vent Port
Sensing PortFlexible Diaphragm
Wiring TerminalsSwitch Contacts
Normal State
(open switch contacts) Activated State (closed switch contacts)
Internal Linkage
Normal State Activated State
Blower Prover
Air Pressure Switch
Normally open contacts,
close on a rise in pressure.
Blocked Exhaust
Air Pressure Switch
Normally closed contacts,
open on a rise in pressure.
Blocked Intake
Air Pressure Switch
Normally closed contacts,
open on a fall in pressure.
Construction
Application & Type

Technical Literature Department 19 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
AIR PRESSURE SWITCHES (CONT)
The water heater covered in this Service Manual is factory equipped with three air pressure
switches. These switches are used to provide verification or prove electrically that the
blower is running and that the vent and intake air pipes are not blocked or restricted. The
switches are located on the top of the water heater as shown in the illustration below.
These switches monitor air pressure through plastic sensing tubes from three different
sensing ports on the water heater. The Blower Prover switch monitors pressure from the
blower’s outlet flange. The Blocked Intake switch monitors pressure from the blower’s intake
air connection fitting. The Blocked Exhaust switch monitors pressure from the exhaust/vent
connection elbow on the bottom of the water heater. See the images below.
TOP VIEW
FRONT
•BLOWER PROVER SWITCH
normally open contacts - close on a rise in pressure
•BLOCKED INTAKE SWITCH
normally closed contacts - open on a fall in pressure
•BLOCKED EXHAUST SWITCH
normally closed contacts - open on a rise in pressure
All switches have SPST(single pole single throw) contacts.
Blocked Intake Switch
Blocked Exhaust Switch Blocked Exhaust Switch Sensing Port
Blower Prover Switch