A.O. Smith Water Heater Error Code 10

Error code 10 means the air pressure switch contacts did not close within 5 seconds of the combustion fan being energized. This tells the control board that proper airflow has not been confirmed, so the ignition sequence is halted as a safety precaution. The fault is most commonly caused by a clogged combustion air intake screen, a failing blower motor, or a defective pressure switch.

The fault code itself is a protective lockout, meaning the heater has stopped operation to prevent ignition without confirmed airflow. This is the safe state. However, the underlying cause, such as a blocked vent or failed blower, should be diagnosed and corrected promptly, since these conditions could allow combustion gases to accumulate if the heater were somehow operated without proper ventilation.

If the intake screen cleaning resolves the issue, the repair costs nothing beyond your time. Replacing the air pressure switch typically runs in the range of $20 to $80 for the part, depending on the model. A blower motor replacement is more involved and can range from $100 to $300 or more for parts, with additional labor costs if a technician is needed.

Start by locating and cleaning the screen on the combustion air intake chamber, as debris buildup is the most frequent cause. After cleaning, reset the heater and observe whether the blower starts and the fault clears. If the error returns, inspect the pressure switch tubing for cracks or disconnections, test the pressure switch for proper continuity, and check the blower motor for weak or erratic operation.

A manual reset will clear the lockout and allow the heater to attempt another startup cycle, but if the underlying cause is not corrected, the code will return within seconds once the blower energizes again. Cleaning the air intake screen before resetting gives the best chance of a successful restart without the fault recurring.