Lennox · Furnace error code

LED1 slow flash + LED2 slow flash (together)Power on, no heat call

Single source Power off, standard tools

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Related diagnostic guides

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

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

Furnace blowing cold air on a heat call

The common causes are a fan set to ON, a dirty filter tripping the high limit so the burners stop while the blower runs, a full condensate drain on a high-efficiency furnace, or an ignition lockout. Gas valve and burner work is blocked; stop at diagnosis and refer.

4 steps ~45 minmoderate

More Lennox furnace codes

Lennox · Furnace

E223

Low pressure switch failed open

Cross-checked High-voltage / caution

Lennox · Furnace

E228

Pressure switch calibration unsuccessful

Single source High-voltage / caution

Lennox · Furnace

E241

Flame sensed out of sequence

Cross-checked Licensed pro only

Lennox · Furnace

E250

Limit switch circuit open

Cross-checked High-voltage / caution

Lennox · Furnace

E290

Igniter circuit fault

Cross-checked High-voltage / caution

Lennox · Furnace

E292

Indoor blower cannot start

Cross-checked High-voltage / caution