Rheem Furnace Code 93
Hard lockout
Internal control fault detected. Either the control's own microprocessor self-test failed, or voltage was found on the main gas valve solenoid when there should be none. The furnace will not operate in any mode. The manual says this should rarely if ever be seen in the field.
Manual wording: “INTERNAL CONTROL FAULT DETECTED ... It is an indicator of an internal microprocessor fault on the furnace control (or I.F.C.) or voltage applied to the main gas valve solenoid when there should be none.”
Documented for: (-)97V, (-)96V, (-)801S/(-)801P
Likely causes, most common first
- 24VAC or similar voltage applied to the main gas valve solenoid circuit unexpectedly
- Furnace control software test failure - failed furnace control (or I.F.C.)
When to call a technician
Call a technician. This is either miswiring on the gas valve circuit or a failed control board, and it cannot be cleared by cycling the heat call.
A Rheem furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Sources
- Installation Instructions for Upflow Condensing Modulating, Communicating Gas Furnaces - (-)97V Series (92-24161-126-04) (Rheem Manufacturing Company, R97V series modulating condensing gas furnace (and R98V); TABLE 18 normal operation codes, TABLE 19 fault codes, pages 94-104) · checked 2026-08-25
- Installation Instructions for 4 Position Condensing Two-Stage, Communicating Gas Furnaces - (-)96V Series (92-24161-124-08) (Rheem Manufacturing Company, R96V series and (-)(-)96MDV two-stage condensing gas furnaces; TABLE 19 normal operation codes, TABLE 20 fault codes, pages 111-120) · checked 2026-08-25
- Installation Instructions for Downflow Single Stage Gas Furnaces - (-)801S / (-)801P Downflow Series (92-24161-143-03) (Rheem Manufacturing Company, R801S, R801P, (-)(-)80DSS, (-)(-)80DSP 80% single-stage gas furnaces; DIAGNOSTICS AND FAULT CODES, page 34) · checked 2026-08-25