Rheem Furnace Code 26
Hard lockout
Line and neutral reversed, or poor ground. The 120V hot and neutral wires feeding the furnace control are swapped, or the control cannot sense a good ground. No heating or cooling will run until it is corrected.
Manual wording: “LINE AND NEUTRAL REVERSED OR POOR GROUND ... This fault code is an indication that line voltage and neutral are reversed to the furnace control or may also be an indication of a grounding issue.”
Documented for: (-)97V, (-)96V, (-)801S/(-)801P
Likely causes, most common first
- Line and neutral to the furnace have been interchanged at the furnace
- Line voltage and neutral have been interchanged at the disconnect or at the breaker box
- Furnace control cannot properly sense ground
When to call a technician
This is line-voltage wiring work. A technician (or an electrician) must meter the supply and correct the polarity and grounding at the furnace, disconnect and panel.
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