York / Coleman / Luxaire · Furnace error code

11 red flashesLimit open 5 to 15 minutes (blower suspected)

Cross-checked High-voltage / caution

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Related diagnostic guides

Guide · Furnace

Field pattern: furnace lights, runs briefly and cycles off (filter and flame sensor before the board)

Two cheap causes account for most of these calls: restricted airflow that trips the high limit, and a coated or misplaced flame sensor that stops proving flame. The common wrong turn is reading 'ignition failure' or 'limit' on the LED, blaming the board and replacing it, while the filter, the sensor rod or the burner ground was the real problem.

8 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

Guide · Furnace

Noisy furnace (squeal, rattle, roar, boom)

Mechanical noises (squeal, grind, rattle) usually come from the blower or inducer and can be checked with power off. A loud boom at ignition or roaring flame is a gas/combustion problem that must be referred.

4 steps ~45 minmoderate