A. O. Smith 5 flashes
A. O. Smith water heater 5 flashes: temperature sensor fault
Short answer
Five flashes means the temperature sensor, a thermistor that tells the gas valve how hot the water is, is defective. A. O. Smith's fix is to turn the gas control knob to OFF and replace the sensor.
The gas control valve cannot heat water safely if it cannot measure the water temperature. When the temperature sensor fails, the valve stops the burner and flashes five times.
The sensor is a thermistor, a part whose electrical resistance changes with temperature. It sits in the tank and connects to the gas valve.
These codes apply to standard atmospheric A. O. Smith gas tanks with a status light on the gas control valve. Power vent, condensing and tankless models use different codes, so check the label on your heater if the pattern does not match.
What to do
- Turn the gas control knob to OFF.
- Have the temperature sensor replaced. A technician may test its resistance first to confirm it has failed.
- If a new sensor does not clear the code, the gas valve itself may be the problem.
Is this a DIY repair?
Replacing the sensor involves working on the gas control and, on some models, draining the tank. It is best handled by a qualified technician.
Common questions
How much does it cost to fix 5 flashes on an A. O. Smith water heater?
The sensor itself is an inexpensive part; most of the cost is the service call and labor. Ask for a quote that covers testing the sensor and the gas valve.
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Other A. O. Smith codes
| Code | Meaning |
|---|---|
| 0 flashes | Light off: pilot out or thermopile not yet warm |
| Solid red | Solid red light: pilot recently went out, thermopile cooling |
| 2 flashes | Pilot lit but thermopile output too low |
| 4 flashes | Water temperature too high (high limit tripped) |
| 5 flashes | Temperature sensor (thermistor) failure |
| 7 flashes | Gas control valve failure |
| 8 flashes | Thermopile still producing power with the knob off (pilot valve may be stuck open) |