These 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.

!! Do Not go by the Fault Descriptions on the blower door - they are extremely misleading !! For example: Code 3 = Pressure Switch Open, but the door description says, "Vent OR termination problem", which is only one (and one of the least common) causes of a Code 3.

Diagnostic Codes:
Slow Green	Normal Operation - no call for heat
Slow Amber	Normal Operation - with a call for HEATING
4 Amber	No Call for G.	Check low voltage wiring
Steady On	Control fault has been detected or there is 24 volts present without 115 volts.	Check that there is 24 volts and 115 volts being supplied to the board. If so, then the board should be replaced.
1 Red	Flame present with gas off	Stuck gas valve Shorted flame sensor Faulty control
2 Red	Pressure switch stuck closed	Bad pressure switch Inducer fan relay stuck on
3 Red	Pressure switch stuck open	Bad pressure switch Bad inducer fan Bad inducer fan relay Blocked or restricted vent Condensate drainage issue
4 Red	Limit switch open / open fuse	Bad limit Low airflow Over-Fired
5 Red	Rollout switch open / open fuse	Bad switch Cracked heat exchanger Bad inducer motor Over-Fired
6 Red	Multiple Code 3's	Bad pressure switch Bad inducer fan Bad inducer fan relay Blocked or restricted vent Condensate drainage issue
7 Red	Ignition lockout due to 3 retries	Bad igniter Dirty flame sensor No gas flow
8 Red	Flame signal lost 5 times	Dirty flame sensor Combustion air problem
9 Red	Grounding or line polarity fault	Try reversing transformer power
10 Red	Gas valve circuit shorted	Check gas valve wiring
11 Red	Extended limit switch open	Bad limit Blower failure

Fault Code Retrieval: With no thermostat call push and release the LAST ERROR button. The LED will flash up to 5 stored fault codes, beginning with the most recent. If there are no codes in memory, the LED will flash two green flashes.

Clear the Fault Codes: Push and hold the LAST ERROR button for at least five seconds. The LED will flash three green flashes when the memory has been cleared.

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Article ID: 578

Last updated: 14 Feb, 2025

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