York Furnace 3 Red Flashes (YP9C Modulating)
Soft lockoutShown as: Three red flashes, two-second pause, repeating
The pressure switch is open while inducer pressure is above the switch setpoint - the switch is open when it should be closed, so the burners cannot light.
Manual wording: “Three Red Flashes - Pressure switch open with inducer pressure above pressure switch setpoint (switch is open when it should be closed). Check pressure switch and pressure transducer.”
Documented for: YP9C, YPLC modulating furnaces
Likely causes, most common first
- Faulty pressure switch
- Faulty pressure transducer
What you can safely check yourself
- Check the outside vent and intake pipe terminations for snow, ice, leaves or nests
- Check the condensate drain and trap for a clog
When to call a technician
If the venting and drain are clear, the pressure switch or transducer needs a technician with a manometer.
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