Lennox · Furnace error code

LED1 slow flash / LED2 onPrimary or secondary limit open

Cross-checked High-voltage / caution

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Related diagnostic guides

Guide · Furnace

Furnace short cycling (starts and stops quickly)

Short cycling is usually a safety opening mid-cycle (limit from low airflow, flame sensor dropping out, pressure switch opening) or a thermostat issue. Read the code and time the cycle.

4 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

Guide · Furnace

Limit trips / overheating (airflow)

The limit protects the heat exchanger from overheating. The fix is almost always airflow: filter, blower, ducts. Rollout switch trips are different and must be referred.

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