Ruud Furnace Code 5
WarningShown as: 5 blinks of the green status LED, repeating
Twin fault (optional feature). Applies only to furnaces wired together in a twinned pair. Rheem's own tech tip also notes the 5-blink code can appear in some cases when an electronic thermostat is used.
Manual wording: “5 Blinks - Twin Fault (Optional)”
Documented for: Standard furnaces with a green status LED and the twinning feature
Likely causes, most common first
- Twinning wiring or dipswitch setting between the two furnace controls is wrong
- The two transformers are not in phase, or the two controls are not the same part number
- On a single (non-twinned) furnace, TWIN not set to the single (OFF) position
- In some cases, an electronic thermostat can trigger this code
What you can safely check yourself
- If you only have one furnace, note the code for your technician - it can point to a thermostat or dipswitch setting issue.
When to call a technician
Twin wiring, transformer phasing and dipswitch settings all have to be checked with power on - technician work.
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