York Furnace 12 Red Flashes (YP9C Modulating)
WarningShown as: Twelve red flashes, two-second pause, repeating
The model ID plug is not present or not connected properly.
Manual wording: “Twelve Red Flashes - ID plug is not present or not connected properly, check for loose plug or loose wires in plug.”
Documented for: YP9C, YPLC modulating furnaces
Likely causes, most common first
- Loose ID plug
- Loose wires in the ID plug
- Missing 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
Have a technician confirm the correct ID plug is fitted and seated - 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 - Modulating ECM Residential Gas Furnace with ECM Motor, Models YP9C*C / TP9C*C / CP9C*C / LP9C*C (Up to 98% Modulating Multi-position), 1083292-UIM-A-0114 (Johnson Controls Unitary Products (York), YP9C*C (York Affinity modulating), and the identical TP9C / CP9C / LP9C chassis) · checked 2026-08-25