A.O. Smith Water Heater Error Code 3

Error code 3 means the water heater attempted to ignite the burner the maximum number of times allowed and failed on each attempt. As a result, the control board has locked out the ignition system for one hour before it will try again. The code points to a problem somewhere in the ignition or gas delivery system. Common culprits include a closed gas valve, low gas pressure, a failed igniter, or a faulty flame sensor.

When error code 3 is active, the burner is not firing and the heater is not producing hot water, so there is no active combustion hazard during the lockout period itself. The lockout is a protective function, not a sign of immediate danger. However, you should not attempt to bypass the control system or force repeated ignition without diagnosing the cause, as a persistent gas supply issue or component failure should be properly addressed.

The one-hour lockout will expire on its own, after which the control board will make another ignition attempt. If that attempt succeeds, the fault code will clear and normal operation will resume. If the underlying problem has not been fixed, the heater will fail to ignite again, accumulate retry failures, and return to the locked-out state with error code 3 displayed again.

The lockout timer is built into the control board and is designed to run for one hour before the unit automatically reattempts ignition. Many A.O. Smith models allow a manual reset by pressing the reset button on the control, which can clear the lockout early. However, if the root cause has not been corrected, the heater will simply run through its retry sequence again and return to the same locked-out state.

Repair costs depend entirely on the root cause. If the fix is simply opening a gas shutoff valve or clearing a vent obstruction, the cost is minimal. Replacing a flame sensor typically runs in the range of $50 to $150 in parts and labor. A gas valve replacement is more involved and can cost anywhere from $200 to $500 or more depending on the model and labor rates in your area.