Ruud Furnace Code 4
Safety faultShown as: 4 blinks of the green status LED, repeating
Pressure switch circuit closed when it should be open - the switch is proving closed before the inducer starts. The manual's checks are the pressure switch contacts, wiring shorts, the control, and water or moisture in the switches and hoses.
Manual wording: “4 Blinks - PS Circuit closed / - Check PS contacts - Check wires for short. - Check IFC. - Check switches and hoses for water or moisture”
Documented for: Standard furnaces with a green status LED, incl. RGRA/RGRB/RGTA/RGRS/RGTS/RGRT
Likely causes, most common first
- Pressure switch contacts stuck or welded closed
- Shorted wiring across the pressure switch
- Water or moisture in the switches and hoses
- Faulty integrated furnace control
What you can safely check yourself
- Nothing safe for a homeowner here - a stuck-closed pressure switch is a combustion safety interlock that is not working.
When to call a technician
Call a technician. A pressure switch that will not open must be replaced, and any field jumper across it must be removed.
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 & Downflow/Horizontal High Efficiency Condensing Gas Furnaces - RGRA/RGRB/RGTA/RGRS/RGTS/RGRT Series (92-24161-16-19) (Rheem Manufacturing Company, RGRA/RGRB/RGTA/RGRS/RGTS/RGRT 90+ condensing furnaces using the UT Electronic Controls 1028-928 integrated furnace control; BLINK CODES (GREEN LED) block on the troubleshooting chart, page 56) · checked 2026-08-25
- Standard Furnace Diagnostic Flash Codes (TP0002) (Rheem Manufacturing Company (Ruud brand), Standard (non-modulating, non-LXE, non-two-stage) gas furnaces with a green status LED) · checked 2026-08-25