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Error code reference
A.O. Smith Water Heater Error Codes
37 error codes documented with diagnostic procedures.
Have your model number? Get codes specific to your unit.
031Incorrect dipswitch settings on the computer board.1Communication error between the upper (electronic control display) and lower (gas control…10Air pressure switch contacts remain open longer than 5 seconds after the combustion fan…101Abnormal combustion detected by the air-fuel ratio detection system.11Flammable Vapor Sensor is open.111Ignition failure12Flammable Vapor Sensor is shorted.121Flame loss13Temperature 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 failure311Output thermistor fault.321Inlet thermistor fault.331Mixing thermistor fault.391Air-fuel ratio rod failure.4Weak flame sensor current.441Flow sensor fault in Easy-Link multi-unit system5Water temperature in the tank has exceeded 185°F (85°C) and has activated the ECO (Energy…510Abnormal main gas valve551Abnormal solenoid gas valves6Air pressure switch contacts remain open longer than 11 seconds after the combustion fan…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 should be…701Computer board fault.721False flame detection741Remote controller communication failure761Communication failure in a multiple heater Easy-Link setup8Open ignitor circuit.9Flammable Vapor Sensor has detected the presence of flammable vapors and the unit is in…991Abnormal combustion
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Step-by-step tests, expected values, wiring diagram references, and verified part numbers.
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Common questions
How do I find the error code on my A.O. Smith Water Heater?
Most A.O. Smith water heaters show the code directly on the control panel display. If your model has no display, it can be read by entering diagnostic mode with the key sequence for your model. The full procedures include model-specific instructions for reading codes.
Are these codes specific to my model?
The codes here apply broadly to A.O. Smith water heaters. Meanings and diagnostic steps can vary by model and production year, so enter your model number for model-specific information and procedures.
What do I do if my code is not listed?
Some codes are model-specific or only appear in diagnostic mode. Enter your model number to get codes specific to your unit, or contact us. We update the database continuously from manufacturer service documentation.
How much does it cost to access the full diagnostic procedures?
A 3-day pass is $9.95 one-time and gives full access to all brands, codes, and procedures. Monthly access is $29/month with unlimited access to everything including Max AI diagnostics.