Lennox SLP98UHV Error Code E 241: Flame Sensed Out of Sequence
What Does Code E 241 Mean?
The E 241 fault on the Lennox SLP98UHV means the flame sensor is detecting a flame signal at a time when the gas valve should be closed and no flame should exist. The SureLight control watches the flame sensor not only to confirm ignition but also to confirm that flame goes out when it is supposed to. Sensing flame out of sequence tells the board that gas may be reaching the burners when it should not be, which is why it treats this as a potentially dangerous condition.
The most likely cause is a gas valve that is leaking through or stuck partially open, letting gas continue to the burners after the valve is commanded shut. That leaking gas can ignite from residual burner heat or another ignition source and keep a flame signal alive. On a modulating furnace the valve is worked hard across its firing range, so a valve that no longer seats fully is the primary suspect behind E 241.
In less common cases, a false flame signal — from a shorted flame-sensor wire, moisture on the sensor, or a control fault — can trigger E 241 without a real flame. Because the consequences of a true gas leak are severe, the code should always be treated as a genuine safety concern until a technician verifies otherwise. If the condition clears on its own, the board follows it with an E 275 soft lockout (flame out of sequence) as a further safety precaution.
What You'll Notice
- The furnace has shut down and displays E 241
- A gas smell near the furnace
- The burners appear to stay lit, or relight, when the furnace should be off
- The furnace refuses to start a normal heat cycle after the fault
- An E 275 soft lockout appearing after the E 241 clears
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Gas valve leaking or stuck open, allowing gas to flow when it should be off | Most common | ✗ Call a pro → |
How This Is Diagnosed
Because E 241 can indicate gas flowing when it should not, a technician's first concern is confirming there is no active gas leak, then leak-testing and inspecting the gas valve to see whether it is seating fully or bleeding through. A valve that does not close tightly is replaced.
Only after the gas side is confirmed safe does the technician rule out a false flame signal — checking the flame sensor and its wiring for shorts or moisture and confirming the control is reading correctly. The furnace is not returned to service until the out-of-sequence flame condition cannot be reproduced.
When to Call a Professional
This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:
- You smell gas near the furnace at any time — shut off the gas supply and treat it as an emergency
- As a homeowner-safe step, turn the manual gas shutoff valve to the furnace to OFF and leave the furnace off until it is inspected
- The furnace has shut down and is displaying E 241
- The code returns after the furnace is reset, or is followed by an E 275 lockout
Frequently Asked Questions
What should I do right now if I see E 241?
Turn the manual gas shutoff valve feeding the furnace to the OFF position and leave the furnace off, then call an HVAC technician. If you smell gas, do not switch anything on or off inside — leave the house and call your gas company or 911 from outside.
Why is E 241 considered dangerous?
It means the furnace is sensing flame when the gas valve should be closed, which can indicate gas leaking past a valve that isn't seating. Because an uncontrolled gas leak is a fire and carbon-monoxide risk, the code is always treated as a real safety concern until a technician confirms the valve is sound.
Could E 241 be a false alarm?
Occasionally a shorted sensor wire, moisture, or a control fault can produce a false flame signal. But because the alternative is a genuine gas leak, it is not safe to assume it's a false alarm — a technician needs to verify the gas valve and sensor circuit before the furnace is used again.
✓ Verified against manufacturer service manual — March 2026