Lennox furnace E275: Soft lockout — flame sensed out of sequence, signal now gone
E275 means the control detected flame when there should have been none, and has locked out for an hour. The flame signal has since gone, but the reason it was there has not been explained.
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
This is the stored counterpart to E241. E241 is the live condition, flame present when it should not be; E275 is the one-hour soft lockout recorded after the signal disappeared. That the signal is gone is not reassurance — it means the condition has stopped being visible, not that it has stopped existing. Lennox's instruction is the same either way: shut off the gas and check for a gas valve leak. The lockout clears when flame has been proven stable, which means a furnace with this in its history can be running normally by the time anyone looks at it, with the underlying valve fault untouched.
Most common causes
- A gas valve leaking through when commanded closed.
- A short in the flame sensing circuit reporting a flame that was not there.
- A burner glowing hot enough after shutdown to generate a brief signal.
- Damaged or shorted flame sensor wiring.
- A failed control board misreading the sense input.
How to diagnose it
- Do not dismiss this because the furnace is running now. The self-clearing behaviour is what makes it easy to ignore.
- If there is any smell of gas, leave the building and call the gas utility from outside.
- Use the code recall menu to check whether this has happened more than once. The control stores the last ten codes.
- Everything else 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 the sense circuit checked for a short.
- A furnace that has recorded this more than once should not be left running while it is investigated.
Notes
The code recall menu is genuinely useful here. A single stored E275 might be explained by a hot burner after shutdown; several of them is a pattern, and only the recall list shows that.
Related
- E241 — Flame sensed out of sequence — flame still present
- Alert code 275 — Flame out of sequence — Watchguard
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.
What the fix costs
The product you are buying against E275 is a ruling-out, and it is cheap relative to what it rules out: a diagnostic visit at $75–150 in which the gas valve is leak-checked answers whether the flame the control saw was real. If the valve is passing gas, the repair is the guide's $300–900 valve replacement — never DIY — and worth every dollar of urgency. If the valve holds tight, the spend shifts to the sensing side at far lower cost, and you have paid $150 for the certainty that your furnace was not burning unmetered gas. The one unacceptable price on this code is zero: because the lockout self-clears once flame proves stable, doing nothing is easy, and it converts a documented safety event into an unexamined one that may be quietly recurring between successful cycles.
DIY or call a pro
E275's homeowner challenge is psychological rather than technical: the furnace is probably running normally by the time anyone reads the code, and every instinct says a fault you cannot see has resolved itself. Follow Lennox's instruction anyway — gas off at the appliance shutoff, system off, professional out promptly — because the stored code is the control testifying that it sensed flame with the valve commanded closed, and the disappearance of the signal is not the disappearance of the cause. Preserve the recall history unconditionally; on a self-clearing code it is the only record the event occurred, and a pattern of E275s at long intervals is precisely the intermittent valve-seepage story a technician needs to see. If E241 — the live version — ever appears while you wait, that is the escalation: the condition is present right now, and the call becomes immediate.
The same fault on other brands
The stored-versus-live split Lennox draws between E275 and E241 is unusual; most families report phantom flame with a single code regardless of whether it is still being sensed — the legacy Goodman/York boards' 1 red flash is typical of the pattern, and the flame sensor hub collects the full 22-code family. The practical consequence of Lennox's split: on this board, a technician can tell from the code alone whether the hazard was momentary or is ongoing, which is exactly the question that sets the urgency everywhere else.
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.