No LED (Off) — Furnace
No power reaching the furnace control board, preventing light-up or self-diagnostics.
Slow Blinking LED — Furnace
Normal furnace operation in standby mode with no heat demand.
Fast Blinking LED — Furnace
Normal furnace operation with an active heat cycle running.
Solid LED (Not Blinking) — Furnace
Furnace control board malfunction or internal hardware fault.
2 Flashes — Furnace
Ignition failure after retries, causing the furnace to lock out.
3 Flashes — Furnace
Pressure switch error due to proper pressure not closing or reopening.
4 Flashes — Furnace
High-limit switch open due to furnace overheating from airflow restriction.
5 Flashes — Furnace
Flame detected while the gas valve is supposed to be off.
6 Flashes — Furnace
Incorrect electrical line polarity or grounding fault detected.
7 Flashes — Furnace
Gas valve circuit error — valve fail to open/close or circuit fault.
8 Flashes — Furnace
Weak flame signal detected, risking unexpected flame loss.
9 Flashes — Furnace
Hot surface igniter failure or incorrect current draw.
22 Flashes — Furnace
Flame instability or abnormal burner flame sensed after ignition.
