What This Error Means

Error code 13 means the burner flame was established and sensed, but the flame signal was then lost during the active heat call. The furnace shuts down and makes another ignition attempt.

Symptoms You May Notice

Burners ignite and run briefly before shutting off; blower continues through an off-delay; inducer performs a post-purge; furnace retries ignition; repeated flame loss may lead to a one-hour lockout.

Common Causes

Dirty, loose, poorly mounted, or poorly grounded flame sensor; damaged flame-sensor wiring; unstable flame pattern; burner assembly installed incorrectly; poor compartment sealing; gas-pressure or combustion instability.

Safe Troubleshooting Steps

1. Turn off furnace power. 2. Inspect the flame sensor and its wire for obvious contamination, looseness, or damage. 3. Confirm the burner and blower access doors are correctly installed and sealed. 4. Review the Flame Sensor Troubleshooting Guide at /flame-sensor-troubleshooting/. 5. Restore power once and observe whether the flame remains stable. 6. A qualified technician should measure flame-sense current, inspect burner flame and crossover, verify gas pressure and grounding, and check compartment seals.

Parts Commonly Involved

Flame sensor; flame-sensor wiring; burner assembly; gas valve; combustion and blower compartment seals; integrated furnace control.

When to Call a Technician

Yes if the flame repeatedly drops out, the furnace enters lockout, or the sensor and access panels appear normal.

Safety Notice

Repeated flame loss can involve gas pressure or combustion problems. Do not alter burners, gas pressure, or safety controls.

Manufacturer Documentation