A.O. Smith 310 - CHECKING THE FLOW SENSOR; FLOW SENSOR TESTING AND CLEANING

TroubleshootingGuide
31|Page
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CHECKINGTHEFLOWSENSOR
Ifthetanklessunitisproperlyconnectedtowater,gas,andpowersuppliesbutthefanmotordoesnot
initiatewhenwaterisrunthroughit,theflowsensorismostlikelynotworkingproperlyandnottelling
thePCBoardtoinitiate.
1) TOOLS
‐Gatherthefollowingmaterialstogether:
a. Degreaserinapumpactionbottle
b. #2PhilipsScrewDriver
c. Flashlight
d. OldTowels,atleastthree
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2) PREPARETHEUNIT
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a. Draintheunitbyfollowingtheproceduresonp.21.
b. Disconnectpowertotheunit.
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3) FRONTCOVER
‐Removethefrontcover.
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4) COMPUTERBOARD
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a. Removethescrewholdingthecomputerboardtothe
manifold,andletthecomputerboardhanginfrontoftheunit
b. Disconnecttheflowsensorwire.
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5) DISCONNECTFROMWATERWAY
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a. Theflowsensorislocatedbehindthecomputerboard.
b. Removethewaterwayclipsoneachsideoftheflowsensorbypushingonthetabs.
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6) CHECKINGTHEFLOWSENSOR
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a. Checkforfunctionality .Flow rateisdeterminedbyanimpellerthatspinsasfluidrunsthrough
it.
b. Blowintotheinletoftheflowsensor.Listenforthespinningimpeller;itshouldspinfreelyfora
fewseconds.Ifitcomestorestabruptlyordoesn’tspinatall,itneedstobecleanedor
replaced.
c. Placetheflowsensorintoacon taineroflemonjuiceoranotherdegreaserfor30minutesand
checkthespinningcapabilityagain. 
d. Testthecleanedflowsensorby“jumping”thesystem:
i. Reattachtheflowsensorwires.
ii. Turnpowerbackontotheunit.(GASSHOULDSTILLBEOFF)
iii. Blowintotheflowsensor;ifthefaninitiates,theflowsensorsuccessfullyreadthe
airflowandshouldnowworkproperly.
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7) REASSEMBLE‐Reassembletheunitinreverseorder.EnsurethattheO‐ringsandwaterwayclipsare
allinplace.
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Figure34