Rheem A001 Error Code: Ignition lockout
Updated October 2026 · Sourced from Rheem documentation
The manual says the heater locked out after a total of 9 consecutive failed ignitions. This disables the heater.
Is it safe to keep running? No. Turn it off and get it checked. If the code returns after one reset, turn it off and call a qualified service provider. Do not keep resetting it. If you smell gas, leave and call your gas supplier.
A001 at a glance
| Code / how it shows | Meaning | Applies to |
|---|---|---|
| A001 Alarm shown on the display | Ignition lockout | Rheem/Ruud/Richmond Residential Super High Efficiency gas tank water heaters with display and EcoNet (Use & Care Manual AP21831) |
Check this first
Only steps a homeowner can do safely. Do not open electrical panels or the burner area.
- Turn the water heater off and back on once at the unit, as the manual says to clear the code.
- Make sure the gas supply valve to the water heater is open.
🛑 Stop and call a licensed pro if
- If the code returns after one reset, turn it off and call a qualified service provider. Do not keep resetting it. If you smell gas, leave and call your gas supplier.
- 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 Rheem 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: Rheem Residential Super High Efficiency Water Heater Use & Care Manual AP21831 Rev 02, Error Codes, p. 42. Codes are series-specific, so your unit's own manual is the final word. Reviewed October 2026.
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