A.O. Smith Water Heater Error Code 631

Error code 631 on an A.O. Smith water heater indicates a pump failure. The control board has detected that the pump connected to the PCB is not operating properly. This could be due to a failed pump motor, a wiring issue, an obstruction, or a faulty control board output. The system flags this fault to prevent damage and alert the user that service is required.

It is not recommended to continue operating the water heater with a pump failure fault active. The pump plays a critical role in water circulation, and running the system without proper pump operation can lead to overheating or damage to internal components. Shut the unit down and have it inspected before resuming use.

Resetting the unit may temporarily clear the fault code, but if the underlying pump problem has not been resolved, the error will return once the control board performs its next pump check. A reset should only be attempted after the pump, wiring, and PCB connections have been inspected and any issues corrected. Do not rely on repeated resets as a substitute for proper diagnosis and repair.

Some basic checks, such as inspecting the wiring connections between the PCB and the pump, can be performed by a knowledgeable DIYer with the power safely shut off. However, testing pump voltage output, diagnosing PCB faults, and replacing components typically require electrical testing tools and familiarity with water heater systems. If you are not comfortable working with electrical components, a qualified technician should handle the repair.

Repair costs depend on the root cause. Pump replacement parts typically range from $50 to $250 depending on the model and pump type, with labor adding $75 to $200 or more. If the PCB is at fault, control board replacement can range from $150 to $400 for the part alone. A technician diagnosis visit may also carry its own service fee.