A.O. Smith Water Heater Error Codes Explained
What the status light on an A.O. Smith gas tank’s electronic control reports, flash by flash, from A.O. Smith’s own service handbook.
Call Now — (717) 470-0340
Which A.O. Smith Water Heaters Show Flash Codes?
A.O. Smith residential standard gas tank water heaters with an electronic gas control valve report their status through a flashing light on the valve. Each code is a count of flashes followed by a three-second pause, repeated.
The codes below come from A.O. Smith’s service handbook for its residential standard gas water heaters, which covers units fitted with a Honeywell electronic gas control valve and thermostat. Source: A.O. Smith, Residential Standard Gas Water Heater Service Handbook, accessed 2026-09-22.
A.O. Smith tankless and hybrid models are outside this handbook and are not covered here. We service A.O. Smith equipment across Harrisburg City and the surrounding communities; the brand service page is A.O. Smith Water Heater Repair in Harrisburg, PA.
What Do the A.O. Smith Status Light Codes Mean?
One flash is normal operation, a solid light means the pilot recently went out, no light means the control is off or the pilot is out, and two, four, five, seven and eight flashes report specific faults. The table below gives each code as A.O. Smith’s handbook names it.
| Status light | What A.O. Smith says it indicates | Normal or fault |
|---|---|---|
| 0 flashes (LED not lit) | Control off, pilot out | Heater off |
| On (solid) | Pilot light was recently extinguished and the thermopile is cooling down | Waiting to relight |
| 1 flash | Normal operation, a bright and dim “heartbeat” | Normal |
| 2 flashes | Thermopile voltage low | Fault |
| 4 flashes | Temperature exceeded (ECO activated) | Fault |
| 5 flashes | Sensor failure | Fault |
| 7 flashes | Internal control failure | Fault |
| 8 flashes | Power off failure | Fault |
There is no three-flash or six-flash code in this handbook. If your unit shows a pattern that is not in the table, the documentation for your specific model is the authority.
What Happens After an A.O. Smith Fault Code Appears?
For four, five and seven flashes, the handbook’s service action is to replace the gas control valve and thermostat; two flashes lead to the thermopile and its wiring; eight flashes lead to the valve. Every one of those actions is gas appliance work for a technician.
Why does four flashes mean a new gas control?
Four flashes report that the temperature limit was exceeded and the ECO activated. A.O. Smith’s handbook resolves it by replacing the gas control valve and thermostat, not by a reset.
What does two flashes point at?
Two flashes report low thermopile voltage. The thermopile and its connections at the gas valve are checked first. A pilot that repeatedly goes out is diagnosed on Water Heater Pilot Light Won’t Stay Lit in Harrisburg, PA.
What does eight flashes mean?
A.O. Smith calls eight flashes a power off failure. It relates to the pilot and the control knob’s off position, and the handbook resolves it at the gas control valve.
The repair scope for all of these sits on Gas Water Heater Repair in Harrisburg, PA.
Why Does an A.O. Smith Status Light Stay Solid After the Pilot Goes Out?
Because the thermopile is still cooling, and A.O. Smith’s handbook states that this gas control has built-in circuitry requiring a 10-minute wait between lighting attempts.
The handbook also notes that the status light will not blink until the thermopile reaches its normal operating temperature, which it says can take up to 90 seconds of continuous pilot operation. A light that has not started blinking straight after a relight is not, on its own, a fault.
Lighting follows the instructions on the water heater’s label. If the pilot will not light or will not hold, stop and call rather than repeating attempts. For other brands, see our water heater guides.
Frequently Asked Questions About A.O. Smith Error Codes
What does 4 flashes mean on an A.O. Smith water heater?
A.O. Smith defines four flashes as temperature exceeded, with the ECO activated. The service handbook resolves it by replacing the gas control valve and thermostat, which is technician work.
What does it mean when the A.O. Smith status light flashes once?
One flash is normal operation. A.O. Smith describes it as a bright and dim heartbeat, and no corrective action is necessary.
What does 2 flashes mean on an A.O. Smith gas water heater?
A.O. Smith defines two flashes as thermopile voltage low. The thermopile and its wiring connections at the gas valve are the first things checked.
Why is the status light on my A.O. Smith solid?
A.O. Smith defines a solid status light as a pilot that was recently extinguished, with the thermopile cooling down. Its handbook states that this control requires a 10-minute wait between lighting attempts.
Do these codes apply to A.O. Smith tankless water heaters?
No. These status light codes come from the A.O. Smith service handbook for residential standard gas tank water heaters. Tankless and hybrid models are outside that handbook.
Get an A.O. Smith Flash Code Diagnosed
Count the flashes between pauses and have the model from the rating plate ready. That is usually enough to bring the right part.
Schedule Service — (717) 470-0340