York Furnace: 13 Flashes
Code 13 red flashes: The high-fire
WarningShown as: Thirteen red flashes, then a two-second pause, repeating
The high-fire (second stage) pressure switch is open when it should be closed. The furnace cannot run on high fire, so on the coldest days it may not keep up.
Manual wording: “13 RED FLASHES: This indicates that the high-fire pressure switch is open when it should be closed. Check for a partially blocked vent pipe or a loose or disconnected wire before replacing pressure switch.”
Documented for: TM9V, TM8V, TM8Y, TM9Y and other two-stage UPG furnaces
Likely causes, most common first
- Partially blocked vent pipe
- Loose or disconnected pressure switch wire
- Broken or disconnected pressure switch hose
- Faulty inducer
- Faulty second-stage pressure switch
What you can safely check yourself
- Check the outside vent and intake pipe terminations for partial blockage from snow, ice, leaves or nests
When to call a technician
If the pipes are clear, the switch, hoses and inducer need to be tested with a manometer by a technician.
A York furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Sources
- Installation Manual - Two Stage Variable Speed ECM Residential Gas Furnaces, TM9V Series (96% AFUE Multi-position), 1083294-UIM-A-0114 (Johnson Controls Unitary Products (York), TM9V*MP two-stage variable-speed ECM 96% AFUE gas furnaces) · checked 2026-08-25
- 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
- Installation Manual - Two Stage Standard ECM Residential Gas Furnaces, TM8Y (80% AFUE Multi-position), 5052632-UIM-D-0217 (Johnson Controls Unitary Products (York), TM8Y*MP two-stage standard ECM 80% AFUE gas furnaces (TM9Y manual 5052617-UIM-G-0817 carries the same table)) · checked 2026-08-25