A.O. Smith Water Heater Error Code 6

Error code 6 means the air pressure switch contacts stayed open for more than 11 seconds after the combustion fan was energized. This tells the control board that sufficient airflow or draft was not confirmed within the required time window. The heater shuts down as a safety precaution until the airflow issue is resolved. The most common cause is a clogged combustion air intake screen.

A power reset by turning the unit off for 10 to 20 seconds and back on will clear the fault code and allow the heater to retry. However, if the underlying cause such as a blocked intake screen or failed pressure switch has not been corrected, the code will return during the next startup attempt. Always address the root cause before relying on a reset.

If the fix is simply cleaning the intake screen, there is no parts cost involved. If the air pressure switch needs replacement, parts typically range from $20 to $60 depending on the model, with professional labor adding $75 to $200 or more depending on local rates. A failed combustion fan motor is a more expensive repair, with parts and labor potentially ranging from $150 to $400. Diagnosing the exact cause before ordering parts can help avoid unnecessary expenses.

Start by cleaning the screen on the combustion air intake chamber to remove any dust, lint, or debris. After cleaning, turn power off for 10 to 20 seconds and then restore power to clear the fault and allow the heater to attempt a new ignition cycle. If the code returns, inspect the pressure sensing tube, check the air pressure switch for continuity, and examine the venting path for blockages. Persistent faults after these steps typically indicate a failed pressure switch or combustion fan motor that needs replacement.

Yes, the air pressure switch is a safety device designed to confirm that combustion air and draft are present before allowing the burner to fire. When the heater displays code 6 and shuts down, it is functioning correctly as a safety measure. Do not attempt to bypass or override the air pressure switch, as doing so could allow combustion without adequate ventilation, creating a carbon monoxide hazard.