Updated 2026-06-25

York Furnace Error Codes & What They Mean

Compiled & reviewed by Nikolai Tsyrenov · Updated 2026-06-25

How do I read York furnace error codes?

York furnaces display a fault as a repeating number of red LED flashes on the control board, with green or amber flashes meaning normal operation.

How to read York furnace codes

York furnaces display a fault as a repeating number of red LED flashes on the control board, with green or amber flashes meaning normal operation. Each red flash is 1/3 second on and 1/3 second off, and the pattern repeats the number equal to the code, separated by a two-second pause (recording the LED on a phone helps). Many boards have a LAST ERROR button that replays the last five stored fault codes when there is no thermostat call. This applies to York and its Johnson Controls sisters (Coleman, Luxaire, Champion).

York furnace code list

CodeWhat it means (tap for fixes)
1 red flashFlame was sensed when there was no call for heat. The control runs the inducer and blower in response.
2 red flashesThe pressure switch is closed when it should be open. The control verifies the contacts are open at the start of each cycle and won't allow ignition if they're stuck closed.
3 red flashesThe pressure-switch contacts are open when they should be closed.
4 red flashesThe main limit switch opened (an over-temperature / airflow condition). The control runs the blower and inducer; if the limit opens five times within one call for heat, the furnace enters a 1-hour soft lockout.
5 red flashesThe limit circuit has been open for more than fifteen minutes, usually indicating a manual-reset rollout switch has opened. This is a hard lockout — power must be cycled off and on after the problem is corrected.
6 red flashesWhile operating, the pressure switch opened four times during the call for heat. The furnace locks out for one hour and then restarts.
7 red flashesFlame could not be established during three trials for ignition. The furnace locks out for one hour and then restarts.
8 red flashesFlame was lost five times (four recycles) during the heating cycle. The furnace locks out for one hour and then restarts.
9 red flashesReversed line-voltage polarity, a grounding problem, or reversed low-voltage transformer wires. Both heating and cooling are affected, and the furnace won't start the ignition sequence until corrected.
10 red flashesThe gas valve is energized with no call for heat. The blower and inducer run and no ignition sequence starts while this condition exists.
11 red flashesThe limit circuit has remained open for more than five minutes (and less than fifteen), usually caused by a failed blower motor or wheel. This is a hard lockout — power must be cycled off and on after the problem is corrected.
4 amber flashesThe control is receiving a thermostat 'Y' (cooling) signal without a 'G' (fan) signal. The furnace still runs normally — this is only a wiring alert; have the 'G' fan wire checked when convenient.
⚠️ Safety first. Gas furnaces burn fuel and produce combustion gases. If you ever smell gas (a rotten-egg or sulfur odor), hear hissing, or your carbon-monoxide alarm sounds, do not touch light switches, thermostats, or the furnace — leave the home immediately and call your gas utility's emergency line or 911 from outside. Homeowners should limit themselves to simple, safe steps: setting the thermostat, checking and replacing the air filter, confirming the furnace switch and breaker are on, keeping supply registers and return grilles open, and clearing snow, ice, or debris from outdoor vent and intake terminations. Never bypass, jumper, or reset safety switches (limit, flame-rollout, or pressure switches), never open the gas valve or burner compartment, and never attempt combustion, electrical, or control-board repairs yourself. Error codes point toward a problem but are not a substitute for proper diagnosis — when in doubt, turn the system off and call a licensed HVAC technician. Keep working carbon-monoxide detectors on every level of your home.

York furnace code FAQ

How do I read the error code on a York furnace?
York furnaces display a fault as a repeating number of red LED flashes on the control board, with green or amber flashes meaning normal operation.
Where is the diagnostic light on a York furnace?
It's on the control board, usually visible through a small sight glass on the lower blower-compartment door. You may need to remove the door panel to read it clearly.
What is the most common York furnace code?
1 red flash — Flame was sensed when there was no call for heat. The control runs the inducer and blower in response.

Other brands

Carrier furnace codesGoodman furnace codesTrane furnace codesLennox furnace codesRheem furnace codesHeil furnace codes

Sources: yorknow.com. General information for homeowners — confirm against your furnace's installation manual.