Lennox · Furnace error code

LED1 on / LED2 onBoard failure or miswiring

Cross-checked High-voltage / caution

Unlock what this code means, its causes, tests and parts

Full library + AI assistant for $34.90, one time.

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

Related diagnostic guides

Guide · Furnace

Furnace runs no heat (blower only or nothing)

Start with the board LED code, then work the call path: thermostat, 24 V, safeties, inducer, ignition, flame proving. Most no-heat calls end at a filter, a flame sensor, a pressure switch issue or gas being off.

5 steps ~45 minmoderate

Guide · Furnace

Blower runs constantly

Check the thermostat fan setting first, then whether the board is holding the blower on for a safety (open limit) or a stuck relay. On electric furnaces a stuck sequencer can do the same.

4 steps ~30 mineasy

Guide · Furnace