York Gas Furnaces Re: Lockout Codes Most York gas furnaces have a control board inside the furnace blower compartment that will flash a diagnostic code that shows the operating status of the furnace. Diagnostic Codes: Slow Green Normal Operation - no call for heat Slow...

York 90% Gas Furnace Re: Flashing Code 3 Flashing Code 3 = Furnace Pressure Switch failed to close on a call for heat. Vent All 90% gas furnaces have a pressure switch to monitor negative pressure from the inducer motor. If the venting system becomes clogged or restricted, the inducer...

York Gas Furnace Re: Flashing Code 1 Code 1 = Flame sensed with no call for heat. ► In a Code 1 situation, the furnace control board thinks that the gas valve is stuck on and the flame is still burning without a call for heat. Therefore, when a control board goes into a code 1, it will lock...