Bradford White U-TW4-75S-76R-3N User Manual
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Manual 238-50629-00A
SERVICE
MANUAL
Troubleshooting Guide
and Instructions for Service
(To be performed ONLY by
qualified service providers)
Models Covered
by This Manual:
U2TW75T*RN
UTW475S76R*N
(*) Denotes Warranty Years
Gas Water Heaters
U TTW 75 Series
®
Bradford White
2
U2TW Series
Gas Water Heaters
Table of Contents
Page U2TW Service Procedure
Introduction 4 - - -
How to Use This Manual 5 - - -
Tool Required for Service 5 - - -
Specifications 6 - - -
Control Timings 8 - - -
Sequence of Operation 9 - - -
Troubleshooting 12 - - -
Burner and Inner Door/Gasket Removal, Inspection
Burner Operation Inspection, Cleaning and Replacement 17 II
Pilot Testing, Cleaning and Replacement 19 III
Pressure Switch Testing and Replacement 20 IV
Blower Testing and Replacement 22 V
Blower Temperature Switch Testing and Replacement 24 VI
Gas Control Testing and Replacement 26 VII
Simulated Resistive Device Testing and Replacement 28 VIII
Resettable Thermal Switch Testing and Replacement 29 IX
Safety Circuit Voltage Trace 31 X
115VAC Circuit Trace 32 XI
Dip Tube Inspection and Replacement 33 XII
Anode Inspection and Replacement 34 XIII
Flue Baffle Inspection and Replacement 35 XIV
Glossary of Terms 36 - - -
Replacement and Reinstallation 14 I
Parts List 39 - - -
Page 2
WARNING: If the information in these instructions is
3
not followed exactly, a fire or explosion may result
causing property damage, personal injury, or death.
Incorrect operation of this appliance may
CAUTION
create a hazard to life and property and
will nullify the warranty.
FOR YOUR SAFETY
Do not store or use gasoline or other flammable,
combustible, or corrosive vapors and liquids in the
vicinity of this or any other appliance.
WHAT TO DO IF YOU SMELL GAS
Do not try to light any appliance.
x Do not touch any electrical switch; do not use any
phone in your building.
x Immediately call your gas supplier from a neighbor's phone.
Follow the gas supplier's instructions.
x If you cannot reach your gas supplier, call the fire
department.
Installation and service must be performed by a qualified
installer, service agency or the gas supplier.
WARNING
Water heaters are heat producing appliances. To avoid
damage or injury, do not store materials against the
water heater or vent-air intake system. Use proper care
to avoid unnecessary contac
the water heater and vent-air intake components.
UNDER NO CIRCUMSTANCES MUST FLAMMABLE
MATERIALS, SUCH AS GASOLINE OR PAINT THINNER BE
USED OR STORED IN THE VICINITY OF THIS WATER
HEATER, VENT-AIR INTAKE SYSTEM OR IN ANY
LOCATION FROM WHICH FUMES COULD REACH THE
WATER HEATER OR VENT-AIR INTAKE SYSTEM.
t (especially by children) with
CAUTION
If sweat fittings are to be used DO NOT apply heat to the
nipples on top of the water heater. Sweat the tubing to
the adapter before fitting the adapter to the water
connections. It is imperative that heat is not appli
the nipples containing a plastic liner.
ed to
WARNING
Hydrogen gas can be produced in an operating water
heater that has not had water drawn from the tank for a
long period of time (generally two weeks or more).
Hydrogen gas is extr
possibility of injury under these conditions, we
recommend the hot water faucet to be open for several
minutes at the kitchen sink before you use any electrical
liance which is connected to the hot water system. If
app
hydrogen is present, there will be an unusual sound such
as air escaping through the pipes as hot water begins to
flow. Do not sm
at the time it is open.
emely flammable. To prevent the
oke or have open flame near the faucet
Do not store or use gasoline or other
flammable, combustible, or corrosive
vapors and liquids in the vicinity of this
or any other appliance.
Before proceeding, please inspect the
water heater and its components for
possible damage. DO NOT install any
water heater with damaged components.
If damage is evident then please contact
the supplie
purchased or the manufacturer listed on
the rating plate for replacement parts.
DANGER
IMPORTANT
r where the water heater was
WARNING
DO NOT ATTEMPT TO LIGHT ANY GAS APPLIANCE IF YOU
ARE NOT CERTAIN OF THE FOLLOWING:
x Liquefied petroleum gases/propane gas and natural gas
have an odorant added by the gas supplier that aids in
the detection of the gas.
x Most people recognize this odor as a “sulfur” or “rotten
egg” smell.
x Other conditions, such as “odorant fade” can cause the
odorant to diminish in intensity, or ”fade”, and not be
as readily detectable.
x If you have a diminished sense of smell, or are in any
way unsure of the presence of gas, immediately contact
your gas supplier from a neighbor's telephone.
Gas detectors are available. Contact your gas supplier, or
plumbing professional, for more information.
WARNING
FAILURE TO INSTALL AND MAINTAIN A NEW, LISTED 3/4” X
3/4” TEMPERATURE AND PRESSURE RELIEF VALVE WILL
RELEASE THE MANUFACTURER FROM ANY CLAIM THAT
MIGHT RESULT FROM EXCESSIVE TEMPERATURE AND
PRESSURES.
CAUTION
Turn off or disconnect the electrical power supply to the
water heater before servicing. Label all wires prior to
disconnection when servicing controls. Wiring errors can
cause improper and d
operation after servicing.
angerous operation. Verify proper
Page 3
Introduction
4
The newBradford White U2TW & UTW4water heaters are designed toprovidereliable
performance with enhanced standardfeatures.Newdesign features includereliablespark to
pilot ignition system, enhanceddiagnostics, simplified
and additionalvent lengths.Inaddition, the U2TW & UTW4water heaters provideUltra Low
NOx emissions.
SparktoPilot Ignition System-employing thespark to pilot ignition systempromotes
reliableand cons
istent pilotand main burner ignitionstoprovide hot water on demand.
Integrated Immersion Thermostat/Gas Control Valve with LED -was developedfor ease
of troubleshooting by providing simple diagnostic codes to pinpointaninstallation or
component performance issu
e.
Powerful Blower - will eliminate problems with difficult venting situations.
Quieter and Cooler Blower Operation - blower noise issignificantly reducedfor both
interiorand exteriorenvironments. Cooler operation increases blower life by reducing bearing
wear and noise
.
RuggedWiring Connections - receptacletype connections promote error free wiring.
IncreasedVent Lengths - increasedventing performance isachieved while maintaining
Energy Factor &FHSR performance.
servicing, significantly quiet operation
Page 4
The U2TW & UTW4w
ater heaters use a combustion systemwhere flue gases are combined
with dilution airto reducethe flue gas temperature in the blower. The diluted flue gases are
evacuated to theexteriorthrough low temperature vent materials. The gas control ma
intains
water temperature, ignition sequenceand regulates gas flow. A safetycircuit consisting of a
pressure switch and blower temperature switch verifies proper conditionsexist forsafeand
reliable operation. If asituation outside of normaloperating parameters exi
sts, the gas control
diagnostic LED will flash a codetopositively identify anoperationalissue.
This service manualis designed tofacilitate problemdiagnosisand enhance serviceefficiency.
Please read the service manual completely before atte
mpting service on this new series of
power vent models.
How to Use This Manual
5
It is intended for this manual to be used by qualified service personnel for the primary purpose of
troubleshooting and repair of the Bradford White U2TW Series water heaters. Understanding the
sequence of operation section of this manual will contribute greatly to troubleshooting the water
heater.
The Honeywell WV4462A Electronic Gas Control will display error codes in the event of abnormal
operation. Error codes are listed in the troubleshooting chart beginning on page 12 of this service
manual. The troubleshooting chart will also indicate the probable cause for the error code and
direct the service professional to a service procedure to properly diagnose the abnormal operation.
In some difficult to diagnose conditions, it may be necessary to isolate the heater from the vent
system to determine the problem.
Contact the Bradford White technical support group immediately if diagnosis cannot be made
using the methods described in this service manual.
Tools Required for Service
Manometer:A liquid “U” tube type or a digital type can be used. This device is used to
measure gas and/or air pressure and vacuum.
Multi-Meter:A digital type is strongly recommended. This device is used to measure
electrical values. The meter you select must have the
measure volts AC, volts DC, Amps, micro-amps and ohms.
Electronic Probes: In some cases, standard multi-meter probes will damage or simply
not be effective to obtain certain voltage and ohm reading. It will be
necessary to have special electronic “pin” type multi-meter probes.
These probes are available at
Thermometer: Used to measure water temperature. An accurate thermometer is
recommended.
Water Pressure Gauge: Used to measure water supply pressure. Also used to determine tank
pressure by adapting to the drain valve of the heater.
Various Hand Tools:Pipe wrench, channel locks, open end wrenchs (3/8",7/16",
12" crescent wrench, Allen wrench set, screw drivers (common &
Phillips), ¼" nut driver, pliers (common & needle nose), socket set, side
cutters wire cutters, wire strippers, wire crimpers, torpedo level, small
shop vac, step ladder, flashlight and 5 gallon pail.
most electronic wholesale outlets.
capability to
½"),
Page 5
Specifications
6
Power supply Dedicated 115VAC, 60 Hz, 15A
Gas Supply Pipe Minimum 1/2" NPT (schedule 40 black iron pipe recommended)
Approved Gas Type Natural.
Gas Pressure 6.0" W.C. min. and 14.0" W.C. max.
Venting System Power vent through the wall or vertical through the roof
Approved Vent Materials PVC, CPVC or ABS
Minimum Clearance
for Servicing
Water Supply Pressure 150 PSI maximum allowable working pressure. Check local codes for supply pressure
Thermal well ECO Limit Residential 188°F (87°C), Commercial 199°F (93°C)
Residential Temperature
Set Point Range
Commercial Temperature
Set Point Range
18" from top, 24" from front, 4" sides and rear.
60°F (16°C) to 160°F (71°C) (Approximate temperatures)
80°F (27°C) to 180°F (82°C)(Approximate temperatures)
Blower Temperature Switch Normally closed, opens @ 165°F (74°C), auto reset @ 130°F (54°C).
Pressure switch
Blower
U2TW75 and UTW475S Models:
Normally open, closes on vacuum increase @-1.28, opens on vacuum decrease @-1.25
U2TW75 and UTW475S Models:
115VAC, 60Hz, 3.1 amps, 3000 RPM,68 CFM@0.4" W.C.
Page 6
Venting Specifications:
7
Specifications
Vent Tables
3" Diameter (7.6 cm) PVC Vent Connector Lengths
Terminating
Through the Wall
# of
Elbows
1 45(13.7) 2 (.6)
Maximum
Length ft (m)
Minimum
Length ft (m)
Through the Wall 2 40(12.2) 2 (.6)
Through the Wall 3 35 (10.7) 2 (.6)
Through the Wall 4 30 (9.1) 2 (.6)
Through the Roof 0 50 (15.2) 7 (2.1)
Through the Roof 1 45(13.7) 7 (2.1)
Through the Roof 2 40(12.2) 7(2.1)
Through the Roof 3 35 (10.7) 7(2.1)
4" Diameter (10.2 cm) PVC Vent Connector Lengths
Terminating
Through the Wall
# of
Elbows
1 175 (53.3) 10 (3.1)
Maximum
Length ft (m)
Minimum
Length ft (m)
Through the Wall 2 170 (51.8) 10(3.1)
Through the Wall 3 165 (50.3) 10(3.1)
Through the Wall 4 160 (48.8) 10(3.1)
Through the Wall 5 155 (47.2) 10(3.1)
Through the Roof 0 180 (54.9) 15 (4.6)
Through the Roof 1 175 (53.3) 15(4.6)
Through the Roof 2 170 (51.8) 15(4.6)
Through the Roof 3 165 (50.3) 15(4.6)
Through the Roof 4 160(48.8) 15(4.6)
Page 7
Specifications
8
Control Timings
Pre-purge 2 Seconds
Trial for Ignition 90 Seconds
Flame Stabilization Period 3 Seconds
Inter-purge 15 Seconds
Flame Failure Response Time 1.5 Seconds (2 second. Maximum; 1 second minimum.)
Post-purge 15 Seconds
PS Fault Delay (failed open/close) Retry after 2 Minutes
Soft Lockout Retry after 5 Minutes
ECO Limit Lockout Indefinite (cycle power to restart)
Verify Resistive Delay Retry after 2 Minutes (repeats 5 times)
Simulated Resistive Load Lockout Indefinite (cycle power to restart)
Hardware Error Lockout Indefinite (self clears if fault clears for at least 15 seconds)
Ignition State Timing
Wiring Diagram
Page 8
Sequence of Operation
9
Power up Sequence
1
Start Up.
Uponpower up, the control runs a safe-start check withatypical start-up delay of 1-5 seconds.
2
SimulatedResistive Load Device Check.
To assure no outputs are energized if the “Simulated Resistive device” is out of range, the control will test the
the device for proper operating range. If the device is within range the control resumes normal operationwith no
perceivable delay. If the device isoutofrange, the control LED immediately flashes 7 times with 3 second pause.
Normal Heating Sequence
1
Thermostat Calls for Heat.
Prior to energizing blower,gas control checks safetycircuittoinsure the circuit isopen. Normal switch positions
in the safetycircuit are as follows:
a) Pressure switch normally open.
b) Blower temperature switch normallyclosed.
If the safetycircuit is
closed, the control waits 4 seconds,gas control LED flashes 2 times with 3 second pause.
Gas control waits 2 minutes then, blower runs for 30 seconds. This cycle repeats until safetycircuitopens.
2
Blower Energizes.
3
Blower Pre-purge Period(2seconds)
4
Pressure Switch Proves Blower/Vent System Operation.
If the pressure switch does not close within 30 seconds, the control LED Flashes 3 times with 3 second pause.
The blower runs for 30 seconds every2minutes trying to get the pressure switchorblower temperature switchto
close. This cycle repeats as long as there isacall for heat.
5
Trial for Pilot Ignition(90 seconds).
a) The gas control lights the pilot by activating spark igniter and gas flow to pilot burner.
b) If flame is not sensedwithin 90 seconds, igniter and gas flow are deactivated, blower will post purgeand
control LED flashes 6 times with 3 second pause.
6
Main Burner Ignition
After pilot flame issensed, gas control activates main valve for main burner ignition. The gas control will ignore
flame and pressure switchsignals for 3 seconds allowing for main burner to stabilize.
Page 9
Sequence ofOperation
10
Normal Heating Sequence (cont.)
Steady State Operation.
7
During Steady State Operation the Control Monitors:
Thermostat temperature sensor- When set point temperature issatisfied,gasvalveis shutdown and
blower will postpurge for 15 seconds. Control LED flashes a short flash onceevery 4 seconds (idle) status
code.
Pressure switch /Blower temperature switch- If either switch opens, pilot valve and main valveis shut
down. The blower continues to runsfor 30 seconds attempting to closethe circuit. The control LED Flashes
3 times with 3 second pause.
Flame Sensor- Ifflameis lost, pilot & main valve are shutdown,blower runsfor 15 seconds.
to re-light pilot 4 times.Ifunsuccessful,Blower is shutdown and control proceeds to 5 minute lockout. Control
re-attempts to light pilot starting at normal heatingsequence#2.
8
Thermostat Satisfies.
9
Burner Off.
10
Blower Post Purge (15 seconds).
Control attempts
Abnormal Operation
1.Simulated ResistiveDeviceFault:
a)Ifthe resistance is greater than 70,000 Ohms - the gascontrol immediately turns off all outputs. Control waits
and monitors resistance for 30 seconds.If theresistanceisgreater than 70,000 ohms after 30 seconds, the
gascontrol proceeds to verifyresistive delay
pause. This process is repeated 5 timesuntil the control either returns to normal operation or proceeds to flashing
7 times with a3second pause.
b) If the resistance is below 3000 ohms - The gascontrol immediately turns off all outp
8 times then once with three second pause. The error selfclears if theresistance returns to normal range for at
least 15 seconds.
for 2minutes and flashes 8 times then once with athree second
uts and proceeds to flash
2. Temperature Sensor Fault:
a) Temperature sensor detected open circuit - The gascontrol Immediately turns off all outputs and proceeds to
flash 8 times then twice with three second pause. The error selfclears if the fault clearsfor at least 15 seconds.
b) Temperature sensors not reading the sametemperature within ±5.5 °F - The gascontrol Immediately t
all outputs and proceeds to flash 8 times then three times with three second pause. The error selfclears if the fault
clearsfor at least 15 seconds.
c) Water temperature in excess of ECO (Energy Cut Out)limit - The gascontrol immediately turns off pilot &
main valve and proc
The set point knobshould beturned to the minimum temperature settingfor at least 6seconds and then turned
clockwise by at least45
Page 10
eeds to flash 4 times with 3 second pause. Blower continues to run until gascontrol is reset.
o
.
urns off
Sequence of Operation
11
Abnormal Operation (cont.)
3. Pressure Switch/Blower Temperature Fault:
a) Pressure switch closed at start of call for heat - Thegas controlwaits four seconds then, proceeds to flash
2 times with 3 second pause.The controlwaits 2 minutes and then turns on blower for 30seconds. Theblower
turns off after 30seconds and the controlwaits for pressure switch to open. Any time the Pressure switch
theblower turns on (or stays on) and the control proceeds to wait for pressure switch to close.
b) Pressure switch or blower temperature switch failed open - Thegas control runs theblower for 30seconds
waiting for the pressure switch and/or blower temperature switch to close.If either sw
seconds,theblower turns off and the control flashes 3 times with 3 second pause.Thegas controlwaits two
minutes before turning on theblower for another 30seconds to see the circuit close.This cycle repeats aslong as
there is acall for heat or
c) Pressure switch or blower temperature switch opens during burner operation - Thegas control turns off the
pilot and main valve, runs blower for 15seconds (inter-purge) waiting for pressure switch and/or blower
temperature switch to close.If either switch fails to close, th
circuit closes again by the end of the inter-purge, the recyclecounter is incremented, if the recyclecount has
not reached itslimit (4), another trial for ignition begins. Ifthe recyclecount has been reached, thegas control
turns off theblower and flashes 6 times then 2 times with 3 second paus
repeating ignition sequence.
until the circuit closes.
e control proceeds as described in 3b above.Ifthe
e.Thegas controlwaits5minutes before
itch does not closein30
opens,
4. Trial For Ignition Fault:
a) Pressure switch opens during trial - Thegas control turns off igniter and pilot valve.Thegas control proceeds
as described in 3b above.Ifthe pressure switch closeswithin 30seconds thegas controlwill continue with trial for
ignition starting at blower pre-purge.
b) Flame Not Sensed - Thegas control energizes the s
flame is not sensed within 90seconds,the igniter turns off, thepilot valve is closed and thegas control runs the
blower through postpurge and flashes 6 times then once with 3 second pause.The controlwaits5minutes before
repeating the ignition sequence.
park igniter attempting to lightthepilot and prove flame.If
5. Flame Sensing Fault:
b) Flame lost during run - Thegas control turns off pilot and main valves,runs blower for 15seconds (inter purge).
Thegas control increments the recyclecount, if the recyclecount has not reached itslimit (4), another trial for
ignition begins. Ifthe recyclecount has been reached, thegas control turns off theblower and fla
then 3 times with 3 second pause.Thegas controlwaits5minutes before repeating the ignition sequence.
c) Flame sensed out of sequence - thegas control only looks for pilot flame when theblower is running.Ifflame is
present when thepilot valve is not open, thegas control proceeds to wait for flame loss
second pause.This continuesuntil flame islost, once theflame signal islost, the control flashes 6 times then 4
times with 3 second pause.The controlwaits5minutes before repeating the ignition sequence.
and flashes 5 times with 3
shes 6 times
Page 11
Troubleshooting
12
Observe green LED indicator on Electronic gas
control. Error flash codes are displayed with a
three second pause before repeating. Check
and repair the system as noted in the
troubleshooting table below.
LED Status
None, control LED not on
or flashing
Short flash, once every
four seconds
“Heartbeat”, alternates
bright/dim
Control Status
No electrical
power
Stand-by mode,
Waiting for call for
heat (no fault)
Thermostat calling
for heat (no fault).
Control power switch in “OFF” position.
Supply voltage interrupted.
Temperature demand is satisfied.
Tank temperature below set point of thermostat.
Probable Cause
Green LED
Indicator
Service
Procedure
Turn power on.
Normal operation.
Adjust thermostat to
temp level.
Normal operation.
Adjust thermostat to
temp level.
Short flash once per
second
Two flash, three second
pause
Three flash, three second
pause
Four flash, three second
pause
Five flash, three second
pause
Page 12
Weak pilot signal
on last call for heat.
Pressure switch not
working-closed
position.
Pressure switch or
blower temp.
switch not working
-open position.
Excessive tank
temperature.
System must be
reset.
Undesired-false
pilot flame present.
1. Unstable pilot.
2. Pilot tube blocked or restricted.
3. Oxidation build up on pilot electrode.
4. Wire damage to pilot assembly or bad
connection at
1. Pressure switch tubing kinked or blocked.
2. Blocked pressure tap on switch or blower.
3. Faulty pressure switch.
1. Vent blockage or improper vent configuration.
2. Pressure switch tubing kinked or blocked.
3. Faulty pressure switch.
4. Blower not spinning up to speed.
5. Blower temp or exhaust temp too high.
6. Faulty blower temperature switch.
1. Thermal well sensor out of calibration.
2. Faulty gas control.
3. Plumbing leak
1. Pilot valve stuck in open position.
gas valve.
1-4. Page 19
Page 20
1. Check vent or vent
tables
2 & 3. Page 20
4. Page 22
5 & 6 Page 23
1-2. Replace gas
control, page 26
Replace gas control,
page 26
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