A.O. Smith T-H2S-DV User manual

TroubleshootingGuide
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CondensingModels
On‐DemandWaterHeater
TroubleshootingGuide
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9/12/11321922‐000
A.O. SmithWaterProductsCompany
500TennesseeWaltzParkway
AshlandCity,TN37015
TollFree:1‐877‐737‐2840
Outdoormodels
(520Outdoor(T‐H2‐DV),
320Outdoor(T‐H2S‐DV))
DirectVentIndoormodels
(520Indoor(T‐H2‐DV),
320Indoor(T‐H2S‐DV))
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

TroubleshootingGuide
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TableofContents
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1. SPECIFICATIONS.…………………………………………………………………………………………………………3
2. INTRODUCTION……………………….………………………………….……..………………………………………4
3. NORMALOPERATION……………………………………………………………………….…………………..……5
Activation……………….…………………………………….………………………………………….…….5
Operation..……………………………………………………………...……………………………………..5
Shutdown…………………………………………………….…….………….……….……………………….5
4. INSTALLATION….…………………………………………………………….……………………………………….….6
Venting……………………………………………………….……….…………………………………….……6
GasLine………………………………………………….…………….…………………………………………6
WaterLine………………………………………………….…………………..…….………………………..7
PowerSupply…………………………………………………...……………………………………………..7
5. TROUBLESHOOTING………………………………………………………….....……………………………………8
PreliminaryChecklist……………………………………………………………..…………………..…..8
GeneralProblems…………………………………………………..…….…………………………………9
ErrorCodes……………………………………………………………………………….………………..….13
Procedures…………………………………………………………..………………………………………….22
VerifyingproperDipswitchsettings……………………………………………….....…22
Drainingtheunit…………………………………………………..……………………………..23
Cleaningthefilter………………………………………………….…………………………….23
CheckingforaCrossConnection………………………………………………….………24
CheckforReverseConnection……………………………………………….…………….24
Checkgassupplypressure……………………………………………….………………….24
Purgethegaslineofair………………………………………………….………………….. 24
Adjustingmanifoldpressure……………………………………………….……………….25
Resettingthecomputerboard……………………………………………….……………26
CheckingtheOHCF……………………………………………….…………………………….26
6. MAINTENANCE……………………………………………………………….…..………………………………………27
RodAssembly………………………………………………………………………………………………..…27
Burner&RodAssembly………………..………………………………….…..……………….………..28
HeatExchanger…………………………………………..……….…..….…………….………….…..…..31
FlowSensor………………………………………………..……..….…………………………………………34
DescalingtheUnit………………………………………..………….……………………………………...35
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TroubleshootingGuide

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Table1:  SPECIFICATIONS‐520(T‐H2)/320(T‐H2S)DirectVentIndoor*andOutdoor 
Model520DirectVent
Indoor(T‐H2‐DV)
520Outdoor
(T‐H2‐OS)
320DirectVent
Indoor(T‐H2S‐DV)
320Outdoor
(T‐H2S‐OS)
DimensionsH25.6"×W18.5"×D12.4"
Weight73lbs.71lbs.73lbs.71lbs.
Combustion
INPUT
BTU/h
Max199,000180,000
Min13,000
CombustionSystemPowervent
InstallationDirect‐ventOutdoorDirect‐ventOutdoor
FanmotorPWMturbofan
Manifold
Pressure**
MaxLP4.9”WC
Natural3.6”WC
LP4.6”WC
Natural2.8”WC
LP4.3”WC
Natural2.5”WC
LP3.6”WC
Natural1.9”WC
MinLP1.0”WC
Natural0.7”WC
LP0.9”WC
Natural0.6”WC
LP1.0”WC
Natural0.7”WC
LP0.9”WC
Natural0.6”WC
Watercontrol
Flowrate0.5GPMto9.0GPM
Availableset
temperatures
100°Fto185°F
default:120°F
Temperatureon
theunitsettings
100°F,105°F,110°F,115°F,120°F,125°F,135°F,140°F,
145°F,150°F,155°F,160°F,165°F,170°F,175°F,185°F
BypassvalveYes
Thermistors4thermistors
(In,Out,Mixing,Exhaust)
3thermistors
(In,Out,Mixing)
4thermistors
(In,Out,Mixing,Exhaust)
3thermistors
(In,Out,Mixing)
Operation
Remotecontroller
modelPart# 9007603005(TM‐RE30)
PCBmodelT‐H2(Part#319143‐126)T‐H2S(Part#319143‐196)
IndicatorsRedLEDonPCBduringoperation&3‐digit7‐SEGLED
Powersupply
controlSurgeabsorber&PowerON‐OFFswitch
Features
FreezeprotectionCeramicheatersandAuto‐firingsystem
Self‐combustion
improvementAir‐FuelRatioDetectionSystem
Easy‐LinksystemYes(Upto4units)N/A
Multiple‐systemN/A
*The520DirectVentIndoor(T‐H2‐DV)and320DirectVentIndoor(T‐H2S‐DV)meansthe520Indoor(T‐H2‐DV)
and320Indoor(T‐H2S‐DV)inthetext.
**Themanifoldpressuremeasurementisbasedonconditionswithoutfrontcover.

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2.INTRODUCTION
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Thismanualprovidesthenecessaryinformationfortroubleshootingthe520(T‐H2)and320(T‐H2S)
tanklesswaterheaters.Thismanualwillbeeffectiveinhelpingyourtroubleshootingneedsaslongas
theinstructionsarefollowedintheintendedorder.Hereishowtousethismanual:
•Firstrefertothe520(T‐H2)and320(T‐H2S)InstallationManualastheprimarysourceof
information.Refertoitalongsidethismanualthroughoutthetroubleshootingprocess.
•Beforetroubleshooting,ifyouareunfamiliarwithhowatanklessunitoperates,readtheNormal
Operationsection(p.5).
•Todouble‐check/troubleshootanewinstallation,usetheProperInstallationsection(p.6).
•Whenbeginningtroubleshooting,firstgothroughthePreliminaryChecklist(p.8);itisdesigned
tofixthemostcommonandfrequentproblems,andprovideyouwithbackgroundinformation
tohelpnarrowdowntheinformationyouneed.
•AfterthePreliminaryChecklist,movetotheErrorCodessection(p.13)ifyouhavereceivedan
errorcode,ortoGeneralProblems(p.9)ifyouhavenotreceivedanerrorcode.
Ifyouhaveanyproblemsorquestionsregardingthisequipment,oratanypointbecomeconfusedor
uncomfortablewithanyoftheprocedures,consultwiththetechnicalservicedepartmentorthelocal
serviceagent.
IMPORTANT
•Installationandservicemustbeperformedbyaqualifiedinstaller(for
example,alicensedplumberorgasfitter).Otherwisethewarrantywill
bevoid.
•Theinstaller/serviceagent(licensedprofessional)isresponsiblefor
correctlyinstallingorservicingyourwaterheaterandforcompliance
withallnational,state/provincial,andlocalcodes.
*ForallunitsinstalledinthestateofMassachusetts,itisrequiredthattheinstallereitherbea
licensedplumberorlicensedgasfitter.
GENERALINSTALLATIONGUIDELINES
1. Followalllocalcodes,orintheabsenceoflocalcodes,followthemostrecenteditionofthe
NationalFuelGasCode:ANSIZ223.1/NFPA54intheUSAorCAN/CSAB149.1NaturalGas,Propane
InstallationCodeinCanada.
2. Properlygroundtheunitinaccordancewithalllocalcodesorintheabsenceoflocalcodes,with
theNationalElectricalCodes:ANSI/NFPA70intheUSAorCSAstandardC22.1CanadaElectrical
CodePart1inCanada.
3. Carefullyplanwhereyouintendtoinstallyourwaterheater.
4. ChecktheratingplateforthecorrectGASTYPE,GASPRESSURE,WATER
PRESSUREandELECTRICRATING.
*Ifthisunitdoesnotmatchyourrequirements,donotinstall.
5. Ifanyproblemshouldoccur,turnoffallhotwatertapsandturnoffthe
gas.Thencallatrainedtechnicianorthegascompany.

WARNING
RATINGPLATE
Figure1

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3.NORMALOPERATION
Becomingfamiliarwithhowatanklesswaterheaternormally
operatesmayhelptotroubleshootit.Assumingitisproperly
installedwithappropriategas,water,andelectric
connections,thefollowingishowitshouldoperate:
1) ACTIVATION
a. Ahotwatertapisopenedenoughthattheflow
sensordetectsaflowratethroughtheheatergreater
thantheactivationpointof0.5gpm.
b. Thefanactivatesafterflowisdetected.
c. Thecomputerchecksforanyproblemswiththeunit
beforestartup.
d. Igniteractivates.Youcanhearthebuzzingofthe
sparkigniter.
e. Maingasvalve,proportionalvalve,andsolenoidgas
valveswillopen.Youwillhearadeep“clunkclunk”
noise.
f. Onceaflameisdetected,theredLEDlocatedon
thecomputerboardwillactivate.
g. Inamulti‐heatersetup,thecontrollerwill
activatethenextheaterin2‐4gpmincrements,
dependingonthesettemperature.
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2) OPERATION
a. Theproportionalgasvalvewillmodulatebasedontheamountofhotwaterdemandedandthe
temperatureriseneeded.Thefanspeedwillmodulateaswelltocreateanefficientburn.
b. Youwillnoticethatonlypartialsectionsoftheburnerwillbelit.Thisisnormaloperation;there
arethreesectionsontheburnerassembly,andthecomputercontrolstheamountofsections
neededbasedontheflowrateandtemperatureriserequired.

3) SHUTDOWN
a. Theheaterwillshutdownwhenthewaterflowratedropsbelowthedeactivationpointof
0.4gpm.
b. Theheaterwillclosethemaingasvalveandsolenoidgasvalves,extinguishingtheflame.
c. WhentheflamedisappearstheredLEDwillturnoff.
d. Thefanwillincreaseinspeedtopurgetheventingofanyremainingexhaustgases.Thelength
ofpost‐purgecanlastupto1½minutes.
e. Theheatergoesintostandbywaitingfortheprocesstobeginagain.

*Thepurposeofthisdiagramistoillustratetanklesswater
heaterdesignconcepts,andmaynotbeaccuratetothe
unit’sphysicaldescription.
Figure2

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*Foreach90degreeelbowadded,deduct5ft.frommax.vent
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4.INSTALLATION
Theseguidelinesarequickoverviewsonthemainpointsofinstallation–Forallinstallationdetails,refer
tothe520(T‐H2)or320(T‐H2S)InstallationManualthatispackagedwitheveryheater.Followallcodes
pertainingtotheinstallationofagasappliance.

VENTING
OUTDOORMODELINSTALLATION:
•OutdoorinstallationsfallundertheDirectVentClearancespublishedbyANSIZ223.1/NFPA54or
CAN/CSA‐B149.1
•Choosealocationthatmeetsallclearancesrequiredbycode.Thetwomostcommonare:
o1ft.fromanyopeningintothebuilding,e.g.doors,windows,etc.
oThetopmustbeatleast3ft.belowasoffit,ventilatedornon‐ventilated,orbelowan
overhang.
INDOORMODELINSTALLATION:
•Refertothefollowingtableforventinglengthmaximums:

Table2
DiameterMax.No.ofElbowMax.Vertical&Horizontal(Total)VentLength
3”225ft.
4”550ft.


•TheventingmayconsistofSchedule40PVC,CPVC,ABS,orCategoryIIIStainlessSteel.
•InCanada,PlasticventingrequiresULCS636Certifiedmaterials.
•DirectVentcombustionairintakeisveryimportant.
oInstalltheDirectVentairintakeopeninginanareathatisfreeofairbornedebris(lint,
grease,dust,flammableliquids,vapors,orchemicals).Dirtyburnertrayandsensorsare
averycommoncauseoftheheateroperatingimproperly.
oFreshairintakepipingmaybemanifoldedusingthefollowingequation:
(newventcross‐sectionalarea)=(numberofheaters)x(5.65)
DONOT:
oCommonventtheexhaustofanytanklessheaterwithanyotherheaterorvented
appliance.
oTerminatetheexhaustintoachimney.Anexistingchimneymaybeusedasachaseto
runexhaustpipeallthewayupandterminatetotheoutside.
oReduceorincreasetheventpipediameterbeyondwhatisspecifiedintheinstallation
manual.
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GASLINE
•Incorrectgastype,NG(Natural)orLP(Propane),isoneofthemostcommonandsimple
problems.Verifythecorrectgastypeby:
oCheckingthatthestampontheburnermanifoldmatchesthegastypesuppliedatthe
applicationsite.
oCheckingtheboxthattheunitcomesinforthegastype.
oMinimumgaslinesizeforthetanklesswaterheateris¾inchpipe. Thesizecanbe
greaterdependingonthedistancetothegasmeterorregulator.
oSizethepipetodeliverthemaximuminletBTU/hrforeachtanklesswaterheater.This
numberis199,000BTU/hourforasingle520(T‐H2),or180,000BTU/hourforasingle
320(T‐H2S).
•Purgethegaslineofair.Seep.23forinstructions.Ifairispresentinthegaslinetheheaterwill
gooffwithanerrorcodeforlossofflame[121]orignitionfailure[111].
•Checkthegassupplypressures.SeetheSpecificationchartonp.1nexttotheTableofContents.
WATERLINE
•Thetanklesswaterheaterrequiresa¾inchconnectiontothecoldwaterinletandhotwater
outlet.
•Tanklesswaterheatersallrequirea“Pressureonly”reliefvalve(PRV)oneachindividualunit
ratedfor150psiwithadischargecapacityofatleasttheratedgasinputofthewaterheater
(199,000BTU/h)tobeinstalledperlocalcode.
•Installa¾”CSA/AGAapprovedisolationvalveoneachheateronallthreeinlets(Hot,Cold,Gas)
fortroubleshootingandmaintenanceprocedures.
•Re‐circulationsystems:
oMinimumflowrateof2.0gpmthroughthesystem.
oAirseparatorandairventinstalledinthesystem.
•Ifsedimentisknowntobeinthewatersupply,aY‐strainermaybeneededtopre‐filter
contaminantspriortoenteringtheheater’scoldwaterinletscreen.
•Forareaswithhardwater,installingawatersoftenerishighlyrecommended.Heatexchanger
damageandfailureduetoscalebuildupcanhappenrapidlyandisnotcoveredbythewarranty.
POWERSUPPLY
•Theunitshouldbeconnectedtoaproperlygrounded120VAC60Hzpowersupply.
•Makesurethataproperdisconnect(i.e.on/offswitch,powerplug,etc.)controllingthemain
powertotheunitisinstalled.
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TroubleshootingGuide
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5.TROUBLESHOOTING
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5.1PRELIMINARY CHECKLIST
Checkallofthesebasicitemsbeforeproceedingontoanyothersection:
•GAS/WATER/ELECTRIC:
oThegassupplyvalveshouldbefullyopen.
oVerifythecorrectgastypeisbeingused,NGorLP.
oThewatersupplyvalveshouldbefullyopen.
oTheunitshouldbeconnectedtoa120VAC60Hzpowersupply.Thiscanbeverifiedby
observingthecomputerboard3‐digitLEDdisplay.Ifitisnotlit,thecomputerboardis
notbeingpowered.ChecktoseeiftheON/OFFswitchbelowthefuseboxissettothe
onposition,orifthefuseinthefuseboxisblown.
•REMOTE:Ifyouareusingaremotecontroller,theremote’spowerbuttonmustbeturnedon.
•HIGHALTITUDE:Isyourlocationatanaltitudeofover3000feet?Thismaycausealackofair.
SeethehighaltitudeprocedureintheTroubleshootingProceduressection.
•HARDWATER:Whatisthehardnessofthewater?Asoftenerisalwaysrecommended,butif
thewaterisabove7grainsofhardnessor70‐140ppm,onemustbeinstalled.Ifthereisno
watersoftenerinstalled,existinginstallationswillgraduallyaccumulatescalebuilduponthe
heatexchangerandcausealeak.Heatexchangerleaksduetohardwaterscalearenotcovered
underthewarranty.
•NEWINSTALLATIONS:Isthisinstallationafewyearsoldorbrandnew?
oAunitthathasworkedproperlyforawhilebutisnowstrugglingmayhavebecome
scaleduporcontainsadirtyburner.
oAnewinstallationismostlikelyinstalledorplumbedincorrectly.
•EXTERNALPROBLEM:Testwhethertheproblemiswithintheunitorexternaltotheunit(i.e.in
theplumbingsystem)byattemptingtorunhotwaterlocallythroughthepressurereliefvalve
(PRV).
oDoestheheaterigniteandremainrunningproperly?Ordoestheheatershutdowninto
anerrorcode?IfitrunsfinethroughthePRVtheplumbingsystemisatfault.

NEXTSTEP:Finally,checktoseeiftheunithasanerrorcode.Theerrorcodewillbedisplayedonthe3‐
digitsevensegmentLEDPCBatthecenteroftheunit.(Seefigure4)
•Ifitisdisplayinganerrorcode,proceedtotheErrorCodessection(p.13).
•Ifthereisnoerrorcode,proceedtotheGeneralProblemssection(p.9).
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5.2TROUBLESHOOTING‐GENERALPROBLEMS
ProceedtotheErrorCodessectionifanerrorcodeisidentified.Forothercommonproblemsthatdo
notinvolveanerrorcode,seeifthefollowingitemshelp:
Thewaterisnothotenough.
Thewateristoohot.
Temperaturefluctuateswhenafixtureisopened.
Unitdoesnotignitewhenwatergoesthroughit.
Ittakesalongtimetogethotwateratthefixtures.
Thefanmotorisstillspinningafteroperationhasstopped.
Abnormalsoundscomefromtheunit.
Lossofpressureatallsinkswhenthedishwasherfills.
Unithaspower,gas,andwaterbutdoesnotturnon.
MultipleHeaterSetup(Easy‐Link)
THEWATERISNOTHOTENOUGH
•Comparetheflowandtemperatureatthepressurereliefvalve.
oIfthetemperatureandflowratearecorrectatthePRVthentheproblemresidesinthe
plumbingline,notinthetanklessunit.
•Testthehotwatertemperaturewithahandheldthermometertomeasurehowfaroffthewater
temperatureisfromthesettemperature.
oThesettemperaturemaybesettoolow.Thetemperaturecanbechangedwiththe
pushbuttonsonthePCBorbytheremotetemperaturecontroller,ifoneisinstalled.
•Checkforcrossplumbingbetweencoldwaterlinesandhotwaterlines.SeetheProcedures
section(p.24)forinstructions.
•Unitmaybehardwaterscaled.Thescaleactsasaninsulatorpreventingtheheatexchanger
fromtransferringheattothewater.Contactaserviceagent.
•Theunitmaynotbereceivingenoughgas.
oThegassupplyvalvemaynotbefullyopen.
oThegaslinemaybesizedimproperly.
oThegassupplypressuremaybetoolow.Thismaybecausedbyamalfunctioninggas
supplyregulator,sochecktoseeifyourregulatorisworkingproperly.
•Checktoseethatacheckvalveisinstalledbetweenthepumpdischargeandtheconnectionto
thecoldwatersupply.Inspectthecheckvalveforproperoperation.Ifthereisn’toneinstalled,
orifitismalfunctioning,coldwatermaybeback‐feedingintothesystem.
•Double‐checkfora101errorcode.A101errorcodewillreducetheamountofgasinputinto
theheater.
•Outputtemperaturewillbeaffectedifairflowisimpeded.
oCheckconstructiondustanddebrisinventing,suchasdrywall.
oIfthereisdustinsidethecabinet,therewillalsobedustinsidetheburnerandheat
exchanger.Seetheprocedureforcleaningtheburner(p.28).
THEWATERISTOOHOT
•Thesettemperaturemaybesettoohigh.Thetemperaturecanbechangedwiththe
pushbuttonsonthePCBorbytheremotetemperaturecontroller,ifoneisinstalled.

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•Theflowadjustmentvalvecouldbeobstructedduetohardwaterscaleordebris,causinglower
thanexpectedwaterflow.Verifywaterflowwithagraduatedcontainerorwiththeremote
temperaturecontroller,ifoneisinstalled.
•Theoutputthermistorcouldbecompromised.Thiscomponentmaybecheckedbyenteringthe
DiagnosticsModeonaremotecontroller,ifoneisinstalled.Turnpowerofftotheunitandrun
coldwaterthroughit;checktoseeiftheinletandoutlettemperaturesreadthesameonthe
remote.Forinstructionsonhowtodothis,refertotheMaintenanceSheet,packagedwith
everytanklesswaterheaterandlocatedbehindthefrontpaneloftheunit.
TEMPERATUREFLUCTUATESWHENAFIXTUREISOPENED
•MakesuretheunitisinstalledproperlyusingtheProperInstallationsection(p.6)ofthisguide.
•Testwhethertheproblemiswithintheunitorexternaltotheunit(i.e.plumbingsystem)by
attemptingtorunhotwaterlocallythroughthePRV.
oDoestheheaterigniteandremainrunningproperly?Ordoestheheatershutdowninto
anerrorcode?
•Plumbingconnections
oCheckforacrossconnection(p.24).
oProblemswitharecirculationsystem:
Checkthatacheckvalveisinstalledbetweenthepumpdischargeandthe
connectiontothecoldwatersupply.
Checktoseeifthepumpisoperatingproperly.
Checkforaircavitation.Thepumpwillbeveryhotorchattering.
Checkthedirectionalindicatoronthepumpflange.
Checkthesizingofthepump–aminimumflowof2gpmisrequired.
•Checkgassupply
oVerifythegassupplylinesaresizedforthemaximumBtu/hdemand,asindicatedinthe
ProperInstallationsection(p.6)ofthisguide.Ifthegassupplylineissharedwithother
appliances,itshouldbesizedtoaccountforthoseappliancesaswell.Theheaterwill
stilltrytorunifthegassupplyisundersizedandhasnowayofdirectlydeterminingif
thereisnotenoughgas.
oForLPmodels,theremaynotbeenoughgasleftinthepropanetank.
oVerifythatthesupplygaspressureiswithinspecification,notonlywhentheheaterisin
standby,butwhiletheheaterisrunningonmaximumfireaswell.
oThegassupplypressuremaybetoolow.Thismaybecausedbyamalfunctioninggas
supplyregulator.
•Venting
oVerifythattheexhaustventingisinstalledtomanufacturer’sspecification.
oVerifythattheventrundoesnotexceedthemaximumlimit(50ft.)
•Thefilteroncoldwaterinletshouldbeclean;lookforsignsofhardwaterscaling.
•Ifthecleartubefromtheproportionalgasvalvetothebottomofthecombustionchamberis
disconnected,fluctuationsintemperatureand/orverylowflowtothefixturesmayoccur.
•Onwellsystemsorevenonsomecitywatersystems,waterpressurefluctuations(especiallyon
lowflow)of8to10psiwillresultinflowratefluctuations,whichwillinturnresultinminor
temperaturefluctuations.
•Flowsensororwatercontrolvalvemaybecompromised.Contactthetechnicalservice
department.
