Run capacitor
Common no-start and weak-compressor failure point. Match the microfarad and voltage rating.
Lennox Error Code 231 — What It Means
Lennox error code 231 indicates a rollout switch fault. The rollout switch is a thermal safety device mounted near the burner compartment. When flames roll out of the heat exchanger — rather than staying contained and traveling into the flue — they heat the rollout switch bimetal element, which opens and kills the gas valve. Code 231 tells you this switch has opened, preventing combustion gases from escaping into the living space.
Common Causes
- Blocked flue or heat exchanger — Soot buildup, bird nests, or a collapsed internal baffle restrict airflow through the heat exchanger, forcing flames to backflow toward the rollout switch.
- Cracked heat exchanger — A crack allows combustion products to bypass the normal flow path and exit where the rollout switch is located.
- Dirty burners — Excess carbon buildup on the burners causes lazy, oversized flames that exceed the heat exchanger inlet and reach the rollout switch.
- Induced draft blower failure — If the draft inducer motor is weak or failing, it cannot pull combustion gases through the heat exchanger efficiently, allowing rollout to occur.
Step-by-Step Fix
- Power down the furnace completely — Turn off the power switch and the gas supply before opening the burner compartment.
- Locate the rollout switch — The rollout switch is a small disc-shaped device with two wires, typically mounted on the burner bracket or vestibule panel above the burners. Some Lennox models have two rollout switches.
- Reset the rollout switch — Many rollout switches have a red manual reset button in the center. Press it firmly until you feel or hear a click. If the button will not reset, the switch has failed or the underlying cause has not been resolved.
- Inspect the burners for flame rollout evidence — Look for soot or scorch marks on the outside of the burner compartment walls, which indicate where flames have been escaping.
- Check the flue and draft inducer — Inspect the flue pipe for blockages. Spin the draft inducer blower wheel by hand (power off) and confirm it turns freely. Reconnect power momentarily and listen for normal inducer operation before burners fire.
- Clean the burners and heat exchanger inlet — Vacuum or brush off carbon deposits from the burner surfaces and the heat exchanger inlet tubes.
- Reset the system — Restore power and gas, and run a full heat cycle. Monitor for rollout switch re-tripping, which indicates the root cause was not resolved.
Parts Often Needed
| Part | Notes |
|---|---|
| Rollout switch (limit switch) | Match to Lennox model number; auto-reset and manual-reset versions exist |
| Draft inducer motor | Replace if motor is noisy, weak, or fails to start |
| Burner assembly / orifices | Replace if burners are corroded or clogged beyond cleaning |
Technician Tips
Lennox furnace error codes are displayed as a series of LED flashes on the SureLight or integrated control board. A slow flash usually indicates normal operation, while rapid flashing points to a specific fault code. Code 1 = no previous code (normal standby). Code 2 = pressure switch failed open — check the vent, condensate drain, and inducer motor. Code 3 = pressure switch failed closed — replace the switch. Code 4 = high temperature limit — check airflow. Lennox systems with the SureLight igniter are particularly sensitive to gas pressure — verify 3.5” WC on natural gas before troubleshooting further. A 5-minute gas pressure check can save an hour of unnecessary component swapping.
Need Replacement Parts?
Before ordering, match the HVAC part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
When to Call a Pro
A cracked heat exchanger is a carbon monoxide hazard and must be diagnosed by a certified HVAC technician using combustion analysis equipment. If rollout switches trip repeatedly after reset, do not continue operating the furnace — call a pro immediately.