Lennox Furnace Code E241: Flame Sensed Out of Sequence Fix

Last updated Sep 23, 2026 · By fixme.vip Editorial

Lennox furnace code E241: what it means

Lennox furnace Code E241 means the control detected flame sensed out of sequence — specifically, the flame sensor still reports a flame after the gas valve has been de-energized (commanded off).

During a normal cycle, once the control drops power to the gas valve the flame should extinguish within a second or two. If the flame-sensing circuit still reads a flame current after that point, the control raises E241 because it can no longer trust that gas flow has actually stopped. That is treated as a safety fault: the furnace assumes either the valve is leaking gas past a closed seat, or the sense circuit is falsely reporting flame.

On most Lennox SureLight and Unitary boards, E241 latches into a lockout that holds until 24 V power is cycled at the disconnect or breaker. The exact wording and whether it soft-locks or hard-locks can vary by board revision, so confirm against the troubleshooting label inside your furnace door.

This is a pro-level code. There is no safe homeowner repair beyond a single reset.

Lennox furnace code E241: common causes, ranked by probability

1. Gas valve not fully closing (valve leak-by). The most serious cause — the valve seat is worn, contaminated, or stuck partly open, so gas keeps feeding a flame after the control shuts it off. This is the failure E241 is designed to catch.
2. Flame sensor giving a false/residual flame signal. A shorted, contaminated, or misrouted flame sensor lead can inject a signal that mimics flame current even when combustion has stopped.
3. Damaged or shorted flame-sensor wiring / connector. A pinched wire or moisture in the connector can bridge the sense circuit to a false reading.
4. Control board fault in the flame-proving circuit. A degraded flame-amplifier input on the board can misread residual signal as active flame.
5. Slow flame extinguishment from crossover/carryover. Burner debris or carbon can let a small flame linger momentarily and be sensed out of sequence, though this is less common than a valve or sensor issue.

Lennox’s own troubleshooting flow for out-of-sequence flame directs the technician to verify whether flame is actually still present first (which isolates a leaking valve) before condemning the sensor or board.

How to fix Lennox furnace code E241: safe checks first

Keep it to these — everything else is inside the cabinet and off-limits:

• Thermostat: Confirm it is calling for heat correctly and, if battery-powered, that the batteries are fresh. Set it to Off while you wait for service.
• Breaker / furnace switch: You may cycle the furnace disconnect or breaker once to attempt a single reset. If E241 returns, stop and call a pro — do not repeatedly reset a lockout.
• Air filter: Check and replace a dirty filter; poor airflow stresses the whole burner cycle. This won’t clear E241 but rules out a contributing airflow problem.
• Visible vents and registers: Make sure supply and return grilles are open and unblocked.
• Condensate line (high-efficiency models): Confirm the drain isn’t obviously clogged or overflowing.

If you ever smell gas — rotten-egg odor near the furnace — leave the house, do not touch switches, and call your gas utility’s emergency line or 911 from outside. E241 can involve a valve that isn’t sealing, so take any gas smell seriously.

How a technician will diagnose it

A qualified tech will typically:

1. Verify actual flame status after the valve is commanded off — visually and with instruments — to confirm whether real flame persists (leaking valve) or the signal is false.
2. Measure flame current (microamps) during and after the burn to see if the sense circuit still reads current after shutoff.
3. Inspect and test the gas valve for leak-by, checking that it fully seats and stops gas flow when de-energized; a valve that passes gas closed is replaced.
4. Check the flame sensor and its wiring/connector for shorts, contamination, moisture, and correct routing.
5. Test the control board’s flame-proving input to rule out a board fault before condemning it.
6. Inspect burners and crossover for debris or carbon that could delay flame extinguishment.
7. Clear the lockout, cycle the furnace, and confirm flame properly extinguishes on shutdown across several cycles.

Because E241 is a gas-safety fault, expect a thorough combustion check — a quote that jumps straight to “replace the board” without testing flame current or the valve deserves a second opinion.

Symptom, cause and what to do

Lennox furnace code E241 repair cost

Honest US ranges, parts and labor combined. Actual prices vary by region and model.

• One-time reset (no fault found): $0 DIY, or a diagnostic fee of $90–$180 if a tech is called out.
• Flame sensor replacement / cleaning: $150–$350.
• Flame-sense wiring or connector repair: $150–$400.
• Gas valve replacement: $400–$700+ — the most likely fix when real flame persists.
• Control board (SureLight/Unitary) replacement: $450–$800+.

If your furnace is under Lennox parts warranty, the component may be covered, but labor usually is not.

Related codes

• Lennox Furnace Code 200: Ignition lockout — flame never proves on startup (opposite failure to E241).
• Lennox Furnace Code E204: Gas Valve Wiring Fix & Cost — miswired or faulty gas-valve circuit.
• Lennox Furnace Code E205: Gas Valve Relay Short Fix — control relay driving the gas valve shorted.
• Lennox Furnace Code E206: Gas Valve Relay Fix & Cost — gas-valve relay failure on the board.
• Lennox Furnace Code E207: Hot Surface Igniter Fix & Cost — ignition component fault.