Coleman Furnace 3 Red Flashes (CP9C Echelon 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.”
Documented for: CP9C Echelon modulating furnaces
Likely causes, most common first
- Faulty pressure switch
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 needs a technician with a manometer.
A Coleman furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- Installation Manual - Residential Gas Furnace with ECM Motor, Models TP9C*C, YP9C*C, CP9C*C, LP9C*C (Up to 98% Modulating Multi-position), 681292-UIM-B-1211 (Johnson Controls Unitary Products (Coleman), CP9C*C Coleman Echelon modulating gas furnace (manual also covers the identical TP9C, YP9C and LP9C chassis)) · checked 2026-08-25