York Furnace 12 Red Flashes
WarningShown as: Twelve red flashes, then a two-second pause, repeating
The model ID plug on the control board is loose or missing. The board uses this plug to know which furnace size it is running.
Manual wording: “12 RED FLASHES: This indicates a loose or missing model ID plug.”
Documented for: TM9V (2017 revision and later), and the modulating YP9C board (Twelve Red Flashes)
Likely causes, most common first
- Loose model ID plug
- Missing model ID plug
What you can safely check yourself
- Turn the furnace off at the service switch for a minute and back on once
When to call a technician
Reseating the ID plug means opening the control compartment. Have a technician confirm the correct plug for the model is installed - the wrong plug makes the furnace fire at the wrong rate.
A York furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- Installation Manual - Two Stage Variable Speed ECM Residential Gas Furnaces, TM9V Series, 5402851-UIM-A-0917 (Johnson Controls Unitary Products (York), TM9V*MP two-stage variable-speed ECM gas furnaces, 2017 revision) · checked 2026-08-25