A.O. Smith 110-310-510 – 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 9.0k? 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.

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