York/Coleman/Luxaire furnace flash codes, decoded
The shared-platform LED language: slow GREEN flash = normal standby, slow AMBER flash = normal heating call. Red fault flashes: 1 = flame detected with gas off (SAFETY), 2 = pressure switch stuck closed, 3 = stuck open (venting/inducer/condensate), 4 = limit open (airflow/filter), 5 = rollout open (SAFETY), 6 = lockout from repeated pressure-switch events, 7 = ignition lockout after retries (auto-resets after ~60 minutes; flame sensor territory), 8 = flame lost repeatedly, 9 = grounding/polarity fault, 10 = gas valve wiring fault (SAFETY), 11 = extended limit (blower suspect), 12 = igniter failure. Steady-ON LED = board fault. Bonus: on many boards, holding the LAST ERROR button 5+ seconds replays/clears the stored code.