# A.O. Smith residential standard gas water heaters error codes

URL: https://costolio.com/home/appliances/a-o-smith/a-o-smith-residential-standard-gas-water-heaters/
Updated: 2026-11-02

# A.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)](https://assets.aosmith.com/damroot/Original/10004/327726.pdf).

## All codes

- [0 flashes](https://costolio.com#0-flashes) LED not lit: control off or pilot out.
- [Solid on](https://costolio.com#solid-on) The pilot was recently put out and the thermopile is cooling.
- [1 flash](https://costolio.com#1-flash) Normal operation.
- [2 flashes](https://costolio.com#2-flashes) Thermopile voltage is low.
- [5 flashes](https://costolio.com#5-flashes) Sensor failure.
- [7 flashes](https://costolio.com#7-flashes) Internal control failure.
- [8 flashes](https://costolio.com#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)](https://assets.aosmith.com/damroot/Original/10004/327726.pdf) (checked 2026-11-02)

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