Lennox furnace E241: Flame sensed out of sequence — flame still present
E241 means the control is reading a flame at a moment when there should be none, and the flame is still there. Lennox's first instruction is to shut off the gas.
Applies to: Lennox gas furnaces with a seven-segment diagnostic display on the control board, such as the ML193UHEK, per installation instructions 508565-01.
What it means
The control checks the flame sensor during windows when the gas valve is closed and nothing should be burning. Reading a flame in that window means one of two things, and one of them is serious: either the gas valve is passing gas when it is commanded shut, or the sensing circuit is reporting a flame that is not there. Lennox does not treat this as a diagnostic puzzle to work through with the furnace running. The published action is to shut off the gas, check for a gas valve leak, and replace the valve if necessary. The distinction between E241 and E275 is whether the flame is still present — E241 is the live condition, E275 is the soft lockout after the signal has gone.
Most common causes
- A gas valve leaking through when it is commanded closed.
- A short in the flame sensing circuit reporting a flame that is not present.
- A burner still glowing hot enough after shutdown to generate a signal.
- Damaged or shorted flame sensor wiring.
- A failed control board misreading the sense input.
How to diagnose it
- Do not work through this before acting. Lennox's own first step is to shut off the gas.
- If there is any smell of gas, leave the building and call the gas utility from outside.
- Note the code before clearing it — E241 and E275 describe the same condition at different stages.
- Everything beyond shutting off the gas belongs to a licensed technician.
How to fix it
- Shut off the gas supply to the furnace at the manual valve.
- Call a licensed technician. This is not a homeowner repair.
- Expect the gas valve to be checked for leak-through, and replaced if it is passing gas.
- Expect the sense circuit and its wiring to be checked for a short as the alternative cause.
Notes
Alert code 250 on the communicating list is the equivalent condition. The number is different between the two Lennox systems, and 250 on the seven-segment list means an open limit circuit instead — see the two-systems page.
Related
- Which Lennox code list applies — Lennox uses two code systems that disagree on code 250
- Alert code 250 — Flame out of sequence — still present
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.