AO Smith 611: Fan Motor Fault
Code 611 on an AO Smith tankless display is the control board reporting a mismatch — it commanded the combustion fan to a certain speed and didn't get the response it expected back.
Applies to: AO Smith tankless/condensing water heaters
What it means
Fan Motor Fault — the combustion fan isn't reaching the speed or voltage the control board expects. The fan's job is to push the exact amount of air through the burner that safe, complete combustion needs, so the board watches it closely; any drag on the motor or break in its wiring shows up here well before you'd notice a difference in hot water performance.
Most common causes
- Dust buildup in the fan or fan housing
- Loose or damaged wiring connections
- Failing fan motor
What you can safely check yourself
- None safe for homeowners — diagnosis requires opening the cabinet and testing wiring/voltages
When to call a professional
Always for this code.
Opening the unit's cabinet and testing fan motor wiring involves line-voltage electrical components and should be done by a licensed HVAC technician or electrician with power off.
What the fix costs
Fan and blower motor replacements on tankless units generally run $200–$500 installed, based on the HomeGuide and Angi contractor rate ranges for water heater component repairs. If the issue turns out to be a simple wiring connection rather than a failed motor, the visit can land closer to the low end of that range. As with any electrical-component repair, get a written estimate before work starts.
Related codes
All AO Smith codes
Every AO Smith water heater fault code — the full list on one page. A failed fan can cut off hot water entirely until it's fixed — see no hot water from a tankless water heater for the broader troubleshooting path.
Sources
- AO Smith tankless water heater error code guide (manufacturer documentation)