Bradford White U2TW75T*RN 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
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
Replacement and Reinstallation 14 I
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 - - -
Parts List 39 - - -
Page 2
2

WARNING: If the information in these instructions is
not followed exactly, a fire or explosion may result
causing property damage, personal injury, or death.
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.
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.
CAUTION
Incorrect operation of this appliance may
create a hazard to life and property and
will nullify the warranty.
DANGER
Do not store or use gasoline or other
flammable, combustible, or corrosive
vapors and liquids in the vicinity of this
or any other appliance.
IMPORTANT
Beforeproceeding, please inspectthe
water heater and its components for
possible damage. DO NOT install any
water heater with damaged components.
Ifdamage isevident then please contact
thesupplier wherethewater heater was
purchased or themanufacturer listed on
therating plate for replacement parts.
WARNING
Water heatersareheat producing appliances. To avoid
damage or injury, donot storematerials against the
water heater or vent-air intakesystem. Use proper care
to avoid unnecessary contact(especially by children) with
thewater heater and vent-air intakecomponents.
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.
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.
CAUTION
Ifsweat fittings areto be used DO NOT apply heat to the
nipples on top of thewater heater. Sweat thetubing to
theadapter beforefitting theadapter to thewater
connections. Itisimperativethat heat isnot applied to
thenipples containing aplastic liner. 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.
WARNING
Hydrogen gas can be produced inan operating water
heater that has not had water drawnfrom thetank for a
long period of time(generally twoweeksor more).
Hydrogen gas isextremely flammable. To prevent the
possibility of injury under these conditions, we
recommend thehot water faucet to be open for several
minutes at thekitchen sink beforeyou use any electrical
appliancewhich isconnected to thehot water system. If
hydrogen ispresent, therewill be an unusual sound such
as air escaping through thepipes as hot water begins to
flow. Donot smokeor haveopen flamenear thefaucet
at thetimeitisopen.
CAUTION
Turnoff or disconnecttheelectrical power supply to the
water heater beforeservicing. Label all wires prior to
disconnection when servicing controls. Wiring errorscan
cause improper and dangerousoperation. Verify proper
operation after servicing.
Page 3
3

Page4
Introduction
ThenewBradfordWhite U2TW &UTW4water heaters are designedtoprovidereliable
performancewithenhancedstandardfeatures.Newdesign features includereliablesparkto
pilotignition system, enhanceddiagnostics,simplifiedservicing, significantly quiet operation
and additionalventlengths.Inaddition, the U2TW &UTW4water heaters provideUltra Low
NOx emissions.
SparktoPilot Ignition System-employing thesparkto pilotignition systempromotes
reliableand consistentpilotand main burner ignitionstoprovidehotwater on demand.
Integrated Immersion Thermostat/GasControl Valvewith LED -was developedfor ease
of troubleshooting by providing simplediagnostic codes to pinpointaninstallation or
componentperformanceissue.
Powerful Blower -will eliminate problemswith difficultventing situations.
Quieter and Cooler Blower Operation - blower noise issignificantly reducedforboth
interiorand exteriorenvironments. Cooler operation increases blower lifeby reducing bearing
wear and noise.
RuggedWiring Connections-receptacletypeconnectionspromote errorfree wiring.
IncreasedVent Lengths-increasedventing performanceisachieved whilemaintaining
Energy Factor&FHSR performance.
The U2TW &UTW4w
ater heaters useacombustion systemwhere fluegases are combined
with dilution airtoreducethefluegas temperature in theblower.Thediluted fluegases are
evacuatedtotheexteriorthrough low temperature ventmaterials.Thegas control maintains
water temperature, ignition sequenceand regulates gas flow. A safetycircuitconsisting of a
pressure switch and blower temperature switch verifies proper conditionsexist forsafeand
reliableoperation. If asituation outsideof normaloperating parameters exists,thegas control
diagnostic LED will flashacodetopositively identify anoperationalissue.
This servicemanualisdesignedtofacilitate problemdiagnosisand enhance serviceefficiency.
Please readthe servicemanual completely before attempting serviceon thisnewseries of
power ventmodels.
4

Tools Required for Service
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.
Page5
Manometer:Aliquid “U” tube type or adigital type can be used. This device is used to
measure gas and/or air pressure and vacuum.
Multi-Meter:Adigital type is strongly recommended. This device is used to measure
electrical values. The meter you select must have the capability to
measure volts AC, volts DC, Amps, micro-amps and ohms.
Electronic Probes:In some cases, standard multi-meter probes will damageor simply
not be effective to obtain certain voltageand ohm reading.It will be
necessary to have special electronic “pin” type multi-meter probes.
These probes are available at most electronic wholesale outlets.
Thermometer:Used to measure water temperature. Anaccurate 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",½"),
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.
How to Use This Manual
5

Specifications
Thermal well ECO LimitResidential 188°F (87°C), Commercial 199°F (93°C)
Residential Temperature
SetPoint Range60°F (16°C) to160°F (71°C) (Approximatetemperatures)
Blower TemperatureSwitch Normally closed, opens@ 165°F (74°C), autoreset@ 130°F (54°C).
BlowerU2TW75 and UTW475SModels:
115VAC, 60Hz,3.1 amps, 3000 RPM,68C[email protected]" W.C.
Pressureswitch U2TW75 and UTW475SModels:
Normally open, closes on vacuum increase @-1.28, opens on vacuum decrease @-1.25
Power supply Dedicated 115VAC, 60 Hz, 15A
Approved Gas TypeNatural.
VentingSystemPower vent through thewall or vertical through theroof
Approved Vent Materials PVC, CPVCor ABS
Gas Supply PipeMinimum 1/2"NPT(schedule 40 black ironpiperecommended)
Minimum Clearance
for Servicing18" from top, 24" from front, 4" sides and rear.
Water Supply Pressure150 PSI maximum allowable workingpressure. Check local codes for supply pressure
Gas Pressure 6.0"W.C. min. and 14.0"W.C. max.
Commercial Temperature
SetPoint Range80°F (27°C)to 180°F (82°C)(Approximate temperatures)
Page6
6

Specifications
Venting Specifications:
Through the Wall
Terminating # of
Elbows
Maximum
Length ft (m)
Minimum
Length ft (m)
3" Diameter (7.6 cm) PVC Vent Connector Lengths
145(13.7) 2(.6)
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 Wall
Terminating # of
Elbows
Maximum
Length ft (m)
Minimum
Length ft (m)
4" Diameter (10.2 cm) PVC Vent Connector Lengths
1 175(53.3) 10(3.1)
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 Roof 0 50 (15.2) 7 (2.1)
Through the Roof 145(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)
Through the Roof 0 180(54.9) 15(4.6)
Through the Roof 1175 (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 Wall 5 155 (47.2) 10(3.1)
Through the Roof 4 160(48.8) 15(4.6)
Vent Tables
Page 7
7

Control Timings
Ignition State Timing
Pre-purge2Seconds
Trial for Ignition90 Seconds
FlameStabilizationPeriod3Seconds
Inter-purge15Seconds
FlameFailureResponse Time1.5Seconds(2second. Maximum; 1second minimum.)
Post-purge15Seconds
PS FaultDelay (failed open/close)Retry after 2Minutes
Soft LockoutRetry after 5Minutes
ECO LimitLockoutIndefinite(cycle power torestart)
Simulated ResistiveLoad LockoutIndefinite(cycle power torestart)
HardwareError LockoutIndefinite(selfclearsiffaultclearsfor atleast15seconds)
Verify ResistiveDelayRetry after 2Minutes (repeats5times)
Specifications
Page8
WiringDiagram
8

Sequence of Operation
Thermostat Calls for Heat.
Prior to energizing blower,gas control checks safetycircuittoinsure the circuitisopen. Normal switchpositions
in the safetycircuit are as follows:
a) Pressure switchnormallyopen.
b)Blower temperature switchnormallyclosed.
If the safetycircuitisclosed, the control waits 4 seconds,gas control LED flashes 2 times with 3 second pause.
Gas control waits 2minutes then, blower runs for 30 seconds. Thiscycle repeats until safetycircuitopens.
Power up Sequence
1Start Up.
Uponpower up, the control runs a safe-start checkwithatypical start-up delayof 1-5 seconds.
2SimulatedResistive LoadDevice 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 deviceiswithin range the control resumes normal operationwith no
perceivable delay. If the deviceisoutofrange,the control LEDimmediatelyflashes 7 times with 3 second pause.
Normal Heating Sequence
1
2Blower Energizes.
3
Pressure Switch Proves Blower/VentSystem Operation.
If the pressure switchdoes 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. Thiscycle repeats as long as there isacall for heat.
4
Blower Pre-purge Period(2seconds)
5Trial for Pilot Ignition(90 seconds).
a) The gas control lights the pilot by activating spark igniter and gas flowto pilot burner.
b) If flame isnot sensedwithin 90 seconds, igniter and gas floware deactivated, blower will post purgeand
control LED flashes 6 times with 3 second pause.
6Main 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.
Page9
9

Steady State Operation.
DuringSteady State Operation theControl Monitors:
Thermostat temperature sensor-When set point temperature issatisfied,gasvalveis shutdown and
blower will postpurgefor 15seconds.Control LEDflashesashort flash onceevery 4 seconds(idle) status
code.
Pressure switch /Blower temperature switch-Ifeither switch opens, pilot valve and main valveis shut
down. Theblower continuesto runsfor 30 secondsattemptingto closethecircuit. Thecontrol LED Flashes
3 times with3second pause.
Flame Sensor-Ifflameislost,pilot & main valve are shutdown,blower runsfor 15seconds.Control attempts
to re-light pilot 4 times.Ifunsuccessful,Blower is shutdown and control proceedsto5minute lockout. Control
re-attemptsto light pilot startingat normal heatingsequence#2.
Thermostat Satisfies.
Burner Off.
Blower PostPurge(15seconds).
9
8
10
7
Sequence ofOperation
Abnormal Operation
1.Simulated ResistiveDeviceFault:
a)Ifthe resistance is greater than 70,000 Ohms-thegascontrol immediately turnsoff all outputs.Control waits
and monitorsresistancefor 30 seconds.Iftheresistanceisgreater than 70,000 ohms after 30 seconds, the
gascontrol proceedsto verifyresistive delay for 2minutesand flashes8 times then once withathree second
pause. Thisprocess isrepeated 5 timesuntil thecontrol either returnsto normal operation or proceedsto flashing
7 times witha3second pause.
b) If the resistance is below 3000 ohms-Thegascontrol immediately turnsoff all outputsand proceedsto flash
8 times then once withthree second pause. The error selfclearsiftheresistance returnsto normal rangefor at
least15seconds.
Normal HeatingSequence(cont.)
2.Temperature Sensor Fault:
a)Temperature sensor detectedopen circuit -Thegascontrol Immediately turnsoff all outputsand proceedsto
flash 8 times then twice withthree second pause. The error selfclearsifthefault clearsfor at least15seconds.
b) Temperature sensors not readingthe sametemperature within ±5.5 °F - Thegascontrol Immediately turnsoff
all outputsand proceedsto flash 8 times then three times withthree second pause. The error selfclearsifthefault
clearsfor at least15seconds.
c) Water temperature in excess of ECO (Energy Cut Out)limit -Thegascontrol immediately turnsoff pilot &
main valve and proceedsto flash 4 times with3second pause. Blower continuesto rununtil gascontrol isreset.
Theset point knobshould beturned to theminimum temperature settingfor at least6secondsand then turned
clockwiseby at least45
o.
Page10
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