No LED (Off) — Furnace
The furnace control board is receiving no electrical power.
Slow Blinking LED — Furnace
Normal standby mode with no active call for heat from the thermostat.
Fast Blinking LED — Furnace
Normal operation indicating an active heating cycle.
Solid LED (Not Blinking) — Furnace
Control board malfunction or microprocessor lockout.
2 Flashes — Furnace
Ignition failure lockout after failing to establish flame during trial.
3 Flashes — Furnace
Pressure switch circuit failed to close or reopen properly.
4 Flashes — Furnace
High-limit safety switch open due to furnace overheating.
5 Flashes — Furnace
Flame detected while the gas valve is commanded off.
6 Flashes — Furnace
Incorrect electrical line polarity or improper ground detected.
7 Flashes — Furnace
Gas valve circuit malfunction or failure to operate properly.
8 Flashes — Furnace
Weak flame signal detected at the flame sensor.
9 Flashes — Furnace
Hot surface igniter failure or incorrect current draw.
22 Flashes — Furnace
Unstable or abnormal burner flame detected after ignition.
