A.O. Smith 110-310-510 – 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 9.0k? 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.