A.O. Smith 310 - Page 15

TroubleshootingGuide
15|Page
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ERRORCODE311[510(T‐D2)],TWOFLASHES/31[110(T‐KJR2),310(T‐K4) ]
OUTPUTTHERMISTOR
1) Checkthatthewireconnectionsaresecureandfreeofburns
orcuts.Theoutputthermistorislocatedontheheat
exchangerontherightside.

2) Checktheresistancevalue;itshouldbeabout9.0kΩatroom
temperature(about74°F).
3) Cleanthethermistor.
a. Draintheunitofwater.Seep.21. 
b. Removethefastenerholdingtheoutputthermistorand
pulloutthesensorprobe.Cleantheprobetoasilver
finish.Do
notlosetherubbero‐ringthatwrapsaround
thissensor.
c. Replaceandtest.
4) Iftheerrorcodepersists,replacethethermistor.

ERRORCODE321[510(T‐D2)],TWOFLASHES/32[110(T‐KJR2),310(T‐K4) ]
INLETTHERMISTOR
1) Checkthatthewireconnectionsaresecureandfreeofburnsorcuts.Theinletthermistoris
embeddedinthewaterinletconnection.
2) Checktheresistancevalue;itshouldbeabout9.0kΩatroomtemperature(about74°F).
3) Cleanthethermistor.
a. Draintheunitofwater.Seep.
21.
b. Removethecomputerboardtoaccesstheinletthermistor.Thecomputerisfixedinplacebya
singlescrewatthetopoftheboard.
c. Removethescrew,pulloutthesensorprobe.Cleantheprobetoasilverfinish.Donotlosethe
rubbero‐ring
thatwrapsaroundthis
sensor.
d. Replaceandtest.

4) Iftheerrorcodepersists,replacethe
thermistor.

ERRORCODE331[510(T‐D2)]
MIXINGTHERMISTOR
1) Checkthatthewireconnectionsaresecure
andfreeofburnsorcuts.Themixing
thermistorisembeddedin thewateroutletconnection. 
2) Checktheresistancevalue;itshouldbeabout9.0kΩatroomtemperature(about74°F).
3) Cleanthethermistor.
a. Draintheunitofwater.Seep.
21.
b. Removethecomputerboardtoaccessthemixingthermistor.Thecomputeris fixedinplaceby
asinglescrewatthetopoftheboard.
c. Removethescrew,pulloutthesensorprobe.Cleantheprobetoasilverfinish.Donotlosethe
redrubbero‐
ringthatwrapsaroundthissensor.
d. Replaceandtest.
4) Iftheerrorcodepersists,replacethethermistor.
Figure8
Figure9