Lennox E241 Error Code — What It Means
E241 on a Lennox furnace is a flame-sensing fault. The control board has detected flame when it should not be present, or the flame sensor circuit is reporting an abnormal signal. On most Lennox platforms this code is labeled as ‘flame sensor out of sequence’ and points to a problem with the flame sensor itself, its wiring, or the combustion process. The exact wording can vary slightly depending on your furnace model and control board version, but the root issue is always tied to how the board interprets flame presence through the sensor circuit.
Common Causes
- Dirty or oxidized flame sensor rod Carbon buildup or corrosion on the sensor prevents it from generating a stable flame signal, causing the board to register flame out of sequence.
- Sensor misalignment or poor flame engulfment The flame rod is not positioned correctly in the flame path, so it cannot detect flame reliably or picks up intermittent signal.
- Loose or corroded wiring and terminals Poor connections or grounding faults in the flame-sense circuit make the board misread flame presence or create false signals.
- Unstable burner flame or combustion issues Gas supply problems, dirty burners, or improper carryover create erratic flame behavior that confuses the flame-sensing circuit.
- Failed flame sensor The sensor rod itself is cracked, broken, or no longer able to produce a valid rectification signal even when clean and properly positioned.
- Control board fault If the sensor and flame quality are verified good, the board may be misinterpreting the flame signal or have a fault in its sensing circuitry.
Step-by-Step Fix
- Confirm the fault code by reading the LED or display on your furnace control board and checking the code legend in your Lennox manual to verify E241 is active and means flame-sensor fault for your specific model.
- Turn off power and gas to the furnace at the service switch and gas shutoff valve before working on any components.
- Remove and inspect the flame sensor rod, looking for carbon deposits, oxidation, cracks, loose mounting hardware, or misalignment in the burner assembly.
- Clean the sensor with fine-grit emery cloth or a non-abrasive pad, wiping gently along the length of the rod until it is shiny and free of buildup, then reinstall it securely in the correct position.
- Check the flame sensor wiring and ground from the rod to the control board, tightening any loose terminals and inspecting for corrosion or damaged insulation.
- Restore power and gas, run a heat call, and observe the burner flame for steady carryover and proper coverage of the flame rod during ignition.
- Clear the fault and test by cycling the thermostat and confirming the furnace completes a full heat cycle without E241 returning; if the code persists after cleaning and wiring checks, replace the flame sensor and retest before evaluating the control board.
Parts Often Needed
| Part | Notes |
|---|---|
| Flame sensor (flame rod) | Amazon | Order the Lennox OEM sensor for your exact furnace model if cleaning does not resolve the fault. |
| Furnace control board | Amazon | Replace only if the flame sensor, wiring, and combustion quality are verified good but E241 continues to appear. |
| Burner assembly or burner components | Amazon | Needed if flame carryover is poor or burners are heavily contaminated and cleaning does not restore stable combustion. |
| Wiring harness or ground wire | Amazon | Replace corroded or damaged flame-sense circuit wiring if cleaning connectors does not restore continuity. |
When to Call a Pro
Call a licensed HVAC technician if you are not comfortable working around gas appliances, if the fault returns after you have cleaned the sensor and checked wiring, or if you observe abnormal flame behavior such as delayed ignition, rollout, or yellow tipping. A technician has the tools to measure flame signal strength, verify grounding integrity, and safely diagnose control-board faults or combustion problems that require calibration or part replacement. Persistent E241 codes can indicate deeper issues with the board or gas supply that need professional evaluation.