A.O. Smith Water Heater Error Codes

37 error codes for A.O. Smith water heater models. Each links to the full diagnostic procedure from the service manual.

CodeDescription

031Incorrect dipswitch settings on the computer board.1Communication error between the upper (electronic control display) and lower…10Air pressure switch contacts remain open longer than 5 seconds after the…101Abnormal combustion detected by the air-fuel ratio detection system.11Flammable Vapor Sensor is open.111Ignition failure 12Flammable Vapor Sensor is shorted.121Flame loss 13Temperature sensor (thermistor) inside the immersion probe is open.14Temperature sensor (thermistor) inside the immersion probe is shorted.15One or both temperature adjustment buttons are stuck.16No current to Power Anode (P-ANODE OPEN).17Power Anode circuit failure.2Self-diagnostic tests have found a problem with an internal circuit.3Ignition/flame failure 311Output thermistor fault.321Inlet thermistor fault.331Mixing thermistor fault.391Air-fuel ratio rod failure.4Weak flame sensor current.

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031 on my A.O. Smith Water Heater

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Incorrect dipswitch settings on the computer

From Service Manual 162980, p.32:

1.Turn off power supply, remove front cover, and check dipswitch settings on left and right banks against correct positions.

2.Measure line voltage at the power cord terminal block. Expected: 120 VAC (L1 to neutral) or 208 to 240 VAC between L1 and L2 under load.

3.Inspect the cord strain relief and terminal block screws for signs of arcing or heat discoloration. Loose connections here mimic an intermittent power failure to the control board.

Part W10911048

Power cord assembly

441Flow sensor fault in Easy-Link multi-unit system 5Water temperature in the tank has exceeded 185°F (85°C) and has activated the…510Abnormal main gas valve 551Abnormal solenoid gas valves 6Air pressure switch contacts remain open longer than 11 seconds after the…611Abnormal fan motor.631Pump failure.651Abnormal flow adjustment valve (Easy-Link multi-unit system only).661Bypass valve fault.7Air pressure switch contacts remain closed for more than 5 seconds when they…701Computer board fault.721False flame detection 741Remote controller communication failure 761Communication failure in a multiple heater Easy-Link setup 8Open ignitor circuit.9Flammable Vapor Sensor has detected the presence of flammable vapors and the…991Abnormal combustion

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