Ruud Furnace Code 30
Hard lockout
Open fuse. The low-voltage fuse on the furnace control has blown, normally because of a 24VAC short to common or ground somewhere in the low-voltage wiring. Nothing will run until the short is found and the fuse replaced.
Manual wording: “OPEN FUSE ... The fuse has been opened. This usually occurs when there is a 24VAC short to common or ground on the low-votage side of the transformer.”
Documented for: (-)97V, (-)96V
Likely causes, most common first
- An electrical short from low voltage (24VAC) to ground or common has occurred
When to call a technician
A technician must find and repair the short before replacing the fuse - simply swapping the fuse will blow it again and can damage the control.
A Ruud 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 (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
- Installation Instructions for 4 Position Condensing Two-Stage, Communicating Gas Furnaces - (-)96V Series (92-24161-124-08) (Rheem Manufacturing Company (Ruud brand), U96V series and (-)(-)96MDV two-stage condensing gas furnaces; TABLE 19 normal operation codes, TABLE 20 fault codes, pages 111-120) · checked 2026-08-25