A.O. Smith Water Heater Error Code 111

Code 111 means the water heater attempted to ignite the burner three times without success and has locked out to prevent unburned gas accumulation. The control board monitors each ignition attempt and trips this lockout when no flame is confirmed after three tries. The error can result from a tripped hi-limit switch, a gas supply issue, a faulty igniter, a dirty flame sensor, or a defective gas valve. Diagnosing the hi-limit switch first is the recommended starting point.

The lockout triggered by code 111 is itself a safety feature, designed to stop the ignition system before unburned gas can build up to a hazardous level. While the locked-out state is safe, you should not attempt to manually override the lockout or repeatedly reset the unit without identifying the underlying cause. If you smell gas at any point, leave the area, avoid operating any switches, and contact your gas utility before proceeding.

Repair costs depend on the faulty component. If only a hi-limit switch reset is needed, there is no parts cost. Replacing a flame sensor or igniter typically falls in the range of $50 to $200 for parts and labor combined, depending on the technician's rates in your area. A gas valve replacement is a more involved repair and can range from $200 to $500 or more. Getting a diagnosis before authorizing parts replacement helps avoid unnecessary expense.

Start by turning off power to the unit, locating the hi-limit switch, and pressing the white reset button firmly until it clicks. Restore power and test whether the heater fires successfully. If the error returns, check that the gas supply valve is fully open and that gas pressure is adequate. If the unit still fails to ignite, further testing of the flame sensor, igniter, and gas valve will be needed to identify the failed component.

Resetting the hi-limit switch may clear the code if a temperature overload was the cause, allowing the heater to resume normal operation. However, if an igniter, flame sensor, or gas valve problem is causing the repeated ignition failures, the code will return after another three failed attempts. A reset should be treated as a diagnostic step, not a permanent fix, unless the root cause has been confirmed and corrected.