Rheem A01 Error Code — What It Means
The A01 fault code on a Rheem water heater means Maximum Ignition Attempts. The control board tried to light the burner multiple times but could not detect a stable flame, so it locked out for safety. This is an ignition and flame-proving fault specific to the burner light-off sequence, not a generic reset code.
The control system expects to see flame confirmation during each ignition attempt. When it does not get that signal after the allowed number of tries, it displays A01 and stops calling for heat until you correct the problem and reset the unit.
Common Causes
- Gas supply interrupted or inadequate The manual shutoff is closed, the meter is off, or upstream gas pressure is too low during the call for heat.
- Flame sensor dirty or corroded The flame rod cannot prove flame because it is coated with carbon or oxidation, or it is loose in its mount.
- Igniter not sparking or weak spark The spark electrode is cracked, fouled, or gapped incorrectly, or the ignition harness connector is loose or corroded.
- Vent or air intake blockage Restricted combustion airflow or blocked flue prevents proper ignition or keeps the burner from lighting reliably.
- Gas valve failure or wiring fault The gas valve does not open on command, or the wiring between the control board and valve is damaged or disconnected.
- Grounding or control board issue Poor chassis ground or a defective control board stops reliable flame rectification and triggers repeated ignition failures.
Step-by-Step Fix
- Turn off power and gas. Flip the circuit breaker off and close the manual gas shutoff valve before working on the heater.
- Verify the gas supply. Reopen the manual shutoff, confirm the meter is on, and check that other gas appliances in the home are working to rule out upstream supply problems.
- Observe an ignition attempt. Restore power and call for hot water or raise the setpoint to trigger ignition, then watch and listen for sparking and whether the burner lights at all before lockout.
- Inspect and clean the flame sensor. Remove the flame rod, wipe it gently with fine steel wool or a non-abrasive pad, check that it is secure in its bracket, and verify the wire connection is tight.
- Check the igniter and electrode gap. Inspect the spark electrode for cracks or carbon buildup, confirm the gap to the burner (consult your model’s manual for the exact spacing), and clean or replace as needed.
- Examine venting and air intake. Look for nests, lint, or debris in the vent termination and air intake, and clear any blockage; on condensing models also check the condensate drain and trap for clogs.
- Reset and test. Power-cycle the heater by switching the breaker off for thirty seconds, restore power, and confirm the unit completes a normal ignition cycle and holds flame without relocking on A01.
Parts Often Needed
| Part | Notes |
|---|---|
| Rheem flame sensor / flame rod | Amazon | Match the sensor style (straight rod or L-bracket) and connector type to your model year and series. |
| Rheem igniter electrode / spark plug | Amazon | Verify the thread size and lead length; some models use a combined pilot assembly. |
| Rheem gas valve | Amazon | Confirm voltage (24 V or millivolt) and inlet/outlet orientation; valve type varies by heater platform. |
| Rheem control board / ignition module | Amazon | Cross-reference the board part number on the existing label; boards are not interchangeable across all series. |
When to Call a Pro
Call a licensed plumber or gas technician if you are not comfortable working with gas connections, if you cannot safely access the burner chamber, or if the heater continues to lock out on A01 after you have confirmed gas supply and cleaned the flame sensor. A technician has combustion analyzers and multimeters to measure flame-rod microamp current, gas pressure, and control-board outputs. Also call a pro if you smell gas at any point, if the vent system needs modification or repair, or if your local code requires permitted work for any gas-appliance service.