Ruud Furnace Code 65
Warning
Mid pressure switch closed when it should be open. Modulating furnaces use a third (mid) pressure switch to allow the middle firing rates. The furnace still heats, but firing rates between 50% and 65% are forced to 70%.
Manual wording: “MID PRESSURE SWITCH CLOSED, SHOULD BE OPEN ... This fault indicates that the mid pressure switch is electrically closed when it should be open.”
Documented for: (-)97V modulating furnaces only
Likely causes, most common first
- Bad wiring to mid pressure switch
- Bad mid pressure switch
- Bad furnace control
What you can safely check yourself
- Nothing homeowner-serviceable. The furnace will keep heating, just with slightly less firing-rate range.
When to call a technician
A technician needs to check the mid pressure switch wiring and replace the switch or control as needed.
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