Rheem Gas Furnace: R801 Re: Diagnostic & Fault Codes The furnace control comes standard with a 7-segment diagnostic display. During Standby mode (with no faults), the display will read "0". During normal Heating, Cooling or Continuous Fan operation, a letter will be displayed to...

Rheem Gas Furnace: R801 Re: No Ignition - No Fault Codes The furnace control goes through an ignition sequence, but the gas valve does not open and there is no spark. The furnace restarts after each failed attempt, but no fault is displayed. Qty Possible Causes: Bad...