A. O. Smith Water Heater 2 flashes: Thermopile voltage low
Updated October 2026 · Sourced from A. O. Smith documentation
The status light flashing twice indicates low thermopile voltage. The chart says there is not enough power (millivolts) to the gas control valve/thermostat.
Is it safe to keep running? No. Turn it off and get it checked. The chart says to check wiring connections and then replace the thermopile. Call a licensed pro if you are not comfortable doing this.
2 flashes at a glance
| Code / how it shows | Meaning | Applies to |
|---|---|---|
| 2 flashes Gas control valve status light flashes, then a pause | Thermopile voltage low | A. O. Smith Direct Vent Residential Gas tank water heaters (Ultra Low NOx models) with gas control valve/thermostat status light |
Check this first
Only steps a homeowner can do safely. Do not open electrical panels or the burner area.
- Follow the lighting instructions on the front of the water heater, as the chart says, and note any diagnostic codes.
- Do not remove the outer door or touch wiring. If you smell gas, leave and call your gas supplier.
🛑 Stop and call a licensed pro if
- The chart says to check wiring connections and then replace the thermopile. Call a licensed pro if you are not comfortable doing this.
- You smell gas. Leave the house, do not touch switches, and call your gas utility from outside.
- Codes for flame failure, overheating, venting or the control board that return after one reset.
- Water leaking from the heater, the relief valve discharging, or scorching around the burner area.
- A carbon monoxide alarm sounds. Get everyone outside and call 911 or the fire department.
Safe first steps for any A. O. Smith code
- Write down the exact code shown on the controller or the number of status light flashes.
- Turn the water heater power off and back on (or press the reset button the manual describes) once. If the code comes back, stop resetting.
- Make sure the gas supply valve to the heater is open and other gas appliances in the home are working.
- Make sure the cold water supply valve is fully open and hot water taps are not partly closed.
- Look at the outside vent terminal for snow, ice, leaves or anything blocking it (look only).
Source: A. O. Smith Direct Vent Residential Gas Water Heater Installation Instructions and Use & Care Guide (Ultra Low NOx), Status Light Code, p. 21 and 30. Codes are series-specific, so your unit's own manual is the final word. Reviewed October 2026.
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