Ruud Furnace Code 77
Hard lockout
No gas valve feedback signal. The furnace control has lost communication with the modulating gas valve. Gas heat is blocked; cooling still runs.
Manual wording: “NO GAS VALVE FEEDBACK SIGNAL ... This fault indicates that the gas valve is not working properly and has lost communications with the furnace control board.”
Documented for: (-)97V modulating furnaces
Likely causes, most common first
- Bad wiring to gas valve
- Bad gas valve
- Bad furnace control
When to call a technician
Technician only - gas valve wiring and replacement are never homeowner work.
A Ruud furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- Installation Instructions for Upflow Condensing Modulating, Communicating Gas Furnaces - (-)97V Series (92-24161-126-04) (Rheem Manufacturing Company (Ruud brand), U97V series modulating condensing gas furnace (and U98V); TABLE 18 normal operation codes, TABLE 19 fault codes, pages 94-104) · checked 2026-08-25