Heater will not ignite; display shows E01 shortly after a call for heat

Safety First: Turn OFF power at the breaker and shut OFF the gas supply before opening the heater. Allow the unit to cool completely.

• Check gas supply: Verify the gas valve to the heater is fully open and that other gas appliances are working. If gas supply is questionable, contact your gas utility or a licensed gas technician.
• Inspect the igniter: Remove the front panel. Locate the hot surface igniter on the burner tray. Look for cracks, white spots, or heavy soot. If damaged, replace the igniter with a Rheem-compatible hot surface igniter.
• Clean the flame sensor: The flame sensor is usually adjacent to the igniter. Gently clean the metal rod with fine steel wool or emery cloth to remove oxidation. Do not sand aggressively.
• Check wiring connections: Inspect the harness from the ignition control board to the igniter and flame sensor. Reseat any loose connectors and look for burnt or brittle wires.
• Reset and test: Restore power and gas, then reset the heater per the user manual. Call for heat and observe ignition. If E01 returns after cleaning and inspection, the ignition control or gas valve may require professional diagnosis.