CostolioA.O. Smith residential standard gas water heaters error codes
7 water heater error codes for A.O. Smith residential standard gas water heaters, what each one means and what to try, paraphrased from A.O. Smith's own source. Codes vary by model, so confirm in your own manual.
Safety. The handbook warns of fire and explosion: never relight if flammable vapors (gasoline, paint thinner) are nearby; have a qualified technician inspect. Source: Residential Standard Gas Water Heater Service Handbook (A.O. Smith).
All codes
- 0 flashes LED not lit: control off or pilot out.
- Solid on The pilot was recently put out and the thermopile is cooling.
- 1 flash Normal operation.
- 2 flashes Thermopile voltage is low.
- 5 flashes Sensor failure.
- 7 flashes Internal control failure.
- 8 flashes Power off failure.
0 flashes
What it means: LED not lit: control off or pilot out. This one often needs a licensed technician.
What to try
- Call a qualified technician to light the pilot per the water heater's label.
Solid on
What it means: The pilot was recently put out and the thermopile is cooling. This one often needs a licensed technician.
What to try
- Call a qualified technician, as the pilot light was recently extinguished and the thermopile is cooling down.
1 flash
What it means: Normal operation. You can usually fix this yourself.
What to try
- No action needed.
2 flashes
What it means: Thermopile voltage is low. This one often needs a licensed technician.
What to try
- Call a qualified technician to check all wiring connections for loose or damaged wires.
5 flashes
What it means: Sensor failure. This one often needs a licensed technician.
What to try
- Call a qualified technician to turn the gas control valve/thermostat knob to OFF.
7 flashes
What it means: Internal control failure. This one often needs a licensed technician.
What to try
- Call a qualified technician to turn the gas control valve/thermostat knob to OFF and replace the gas control valve/thermostat.
8 flashes
What it means: Power off failure. This one often needs a licensed technician.
What to try
- Call a qualified technician to turn the pilot off, let it cool down for ten minutes and relight it according to the lighting instructions.
Source
- Residential Standard Gas Water Heater Service Handbook (A.O. Smith) (checked 2026-11-02)
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