York Furnace 6 Red Flashes (YP9C Modulating)
Soft lockoutShown as: Six red flashes, two-second pause, repeating
Gas valve communication error. The modulating gas valve and the control board have lost their data link, so the furnace cannot modulate or fire.
Manual wording: “Six Red Flashes - Gas valve communication error.”
Documented for: YP9C, YPLC modulating furnaces
Likely causes, most common first
- Loss of communication between the control board and the modulating gas valve
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
Modulating gas valve communication faults are a technician job - the valve, its harness and the board all have to be checked.
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