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 {#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 | Amazon | Verify correct temp rating — Lennox uses several setpoints |
| Induced draft motor with wheel | Amazon | Replace as assembly if wheel is cracked or motor bearing is worn |
| Vent pipe elbow or section | Amazon | Replace cracked or blocked PVC sections on 90%+ units |
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