York error codes, decoded.

Normal operation — the ignition control board is powered and ready to respond to a heating demand.

LED is steady off — no power to the control, or the control has suffered catastrophic damage.

LED is steady on — the control's microprocessor has not passed its self-check.

Induced draft pressure switch did not close — the switch failed to prove airflow within 10 seconds of the inducer starting.

Induced draft pressure switch stuck closed — the switch reads closed at the same moment a call for heat begins.

Flame could not be established — no flame was sensed in three consecutive ignition attempts (lockout).

Flame loss — an established flame dropped out five times during one heating cycle (lockout).

Open limit — 24 VAC was lost at the limit-switch input for six minutes or less during a call for heat.

Open rollout — 24 VAC was lost at the control's flame rollout switch input.

Gas valve failed to shut off — flame was sensed for more than 2 seconds after the gas valve output was turned off.

Indoor airflow failure / open limit — limit input lost 24 VAC for more than six minutes during a call for heat (hard lockout).

Gas valve miswire or gas valve relay fault — unexpected or missing 24 VAC at the gas valve outputs.