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
Lennox alert code 241 on a communicating system reports the same condition. The two Lennox lists agree on this code.
Related
- Which Lennox code list applies — Lennox uses two code systems, and knowing which you are reading matters
- Alert code 250 — Primary limit switch open
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.
What the fix costs
Lennox's action line prices this code itself: shut off gas, check for gas valve leak, replace if necessary — and a gas valve is $300–900 installed, in the category the repair guide marks never-DIY without exception. What the seven-segment board contributes to the bill is speed: its flame signal mode displays live microamps, so a technician can watch the flame current with the valve commanded closed and distinguish the two suspects directly — real current from a real flame that should not exist (the valve), or a sensing anomaly reporting one (the cheaper electrical repair). That observability keeps the diagnostic tight, typically inside the standard $75–150, and stops the expensive guess of replacing a healthy valve to silence a sensing ghost — or worse, the reverse.
DIY or call a pro
The homeowner instruction set for E241 is short and sequenced, and step one is not a diagnosis: close the appliance gas shutoff, switch the furnace off, and make the call today. This code means the control saw flame in a window when its valve was commanded closed and the flame is still being sensed — of the E-code list, it is the one where waiting has the least defense. Do not run test cycles from the thermostat, do not clear the code, and treat any gas smell as a reason to leave and call the utility's emergency line before the HVAC company. There is no meter check, panel inspection or visual confirmation on this one that improves the situation from the homeowner side; the entire value you can add is making the furnace safe-off quickly and reporting accurately whether the burners were visibly lit or the cabinet warm when no heat was called.
The same fault on other brands
Every major control family reserves a code for flame out of sequence — the flame sensor hub counts 22 across 11 families. The closest E-code peers are Trane's E05 on the S9V2 display and Goodman's E4 on its seven-segment boards, with Allied's 12 flashes covering the Armstrong/AirEase/Concord/Ducane lineage. Like Lennox, most of them pair a live version with a stored one; here the stored counterpart is E275.
What this looks like
From the outside, this usually shows up as the burner lights and then drops out a few seconds later — that walkthrough covers what to check in order, and when it stops being a homeowner job.