Run capacitor
Common no-start and weak-compressor failure point. Match the microfarad and voltage rating.
Lennox Error Code 111 — What It Means
Lennox fault code 111 (three flashes on the diagnostic LED, or displayed as “111” on SureLight boards) indicates the rollout switch has opened. The rollout switch is a thermal fuse-type safety device positioned near the burner orifices or heat exchanger opening. It trips when combustion gases or flame exit the heat exchanger in an uncontrolled direction — a condition called flame rollout. This is a hard safety event: the furnace shuts down completely and will not restart until the switch is manually reset and the root cause is addressed.
Common Causes
- Restricted flue or venting — A partially blocked or fully blocked flue prevents combustion gases from exiting normally, creating back pressure that reverses flow and causes rollout.
- Induced draft motor failure — If the inducer wheel is broken, the motor is failing, or the bearing is worn, draft is insufficient to keep combustion contained within the heat exchanger.
- Cracked heat exchanger — Cracks in the primary or secondary heat exchanger allow combustion gases to bypass the normal flow path and contact the rollout switch. A critical safety finding.
- Incorrect gas pressure — High manifold gas pressure produces an oversized flame that can exceed the heat exchanger capacity and roll out past the burner opening.
Step-by-Step Fix
- Let the switch cool before reset — The rollout switch is temperature-actuated. It won’t reset until it drops below its reset threshold (typically well below 200°F). Wait at least 10–15 minutes after shutdown.
- Inspect the flue from furnace to termination — Check PVC vent pipes on 90%+ units or metal flue on 80% units. Look for sagging pipe that traps condensate, blocked termination screens, or critter intrusion.
- Verify inducer operation — Start the furnace and observe the inducer. It should ramp up and reach full speed within a few seconds. Sluggish start or intermittent operation indicates a motor or capacitor problem.
- Reset the rollout switch — Locate the manual-reset button (often red) on the burner compartment wall near the heat exchanger opening. Press firmly until it clicks.
- Check manifold gas pressure — Connect a manometer to the gas valve outlet port. Verify pressure matches the spec on the furnace rating plate (typically 3.5” W.C. for natural gas).
Parts Often Needed
| Part | Notes |
|---|---|
| Rollout limit switch | Verify correct temp rating — Lennox uses several setpoints |
| Induced draft motor with wheel | Replace as assembly if wheel is cracked or motor bearing is worn |
| Vent pipe elbow or section | Replace cracked or blocked PVC sections on 90%+ units |
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
Flame rollout combined with a cracked heat exchanger is a carbon monoxide hazard. If you cannot identify a clear venting or draft cause for the rollout trip, stop operating the furnace and have a technician perform a full combustion and heat exchanger inspection before restart.
See Also
- Lennox Error Code 114 — Causes & Fix
- Lennox Error Code 231 — Causes & Fix
- Lennox Error Code 223 — Causes & Fix
- Lennox G60UHV Furnace Error Codes — Flash Code Diagnostic Guide