York Furnace: 12 Flashes
A York furnace LED pattern starting with 12 flashes matches 2 documented codes: 12 red flashes, 12 red flashes (YP9C modulating). Watch the full pattern (short vs. long flashes) to tell them apart — all 2 are explained below.
Code 12 red flashes: The model ID plug on the control board is loose or missing
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
Code 12 red flashes (YP9C modulating): The model ID plug is not present or not connected properly
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