Lennox E275 Error Code

What does Lennox E275 mean?

E275 is a soft lockout triggered when the Lennox communicating furnace detects flame out of sequence — specifically when a flame signal disappears after being sensed out of sequence (code E241 condition). The furnace enters Watchguard mode. This typically points to a leaking gas valve allowing residual flame after the valve should have closed.

Symptoms

• Furnace enters soft lockout and does not attempt another ignition cycle.
• E275 or 'GF Flame Out Of Seq. No Flame' displayed on the thermostat.
• Flame is detected by the sensor when no gas valve call is present.
• System fails to restart without a power cycle or technician reset.

Common causes

• Leaking or stuck-open gas valve allowing gas flow when the valve should be closed.
• Flame sensor shorted to ground producing a false flame signal.
• Damaged or contaminated gas valve that cannot fully close.
• Incorrect gas valve wiring causing the valve to remain energized.

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Diagnostic steps

1. Shut off gas supply to the furnace

   Turn the manual gas shutoff to the closed position. This eliminates the risk of continued gas flow through a leaking valve while you diagnose.

2. Inspect gas valve wiring and connections

   With power off, verify that all wires to the gas valve terminals match the wiring diagram. A miswired valve can remain energized when it should be closed.

3. Check flame sensor for shorts

   Remove the flame sensor and inspect for cracks, carbon buildup, or contact between the rod and the bracket. Measure resistance between the sensor rod and ground — it should be very high (megohms). A low reading indicates a shorted sensor.

4. Test gas valve operation

   With gas on and valve commanded closed, check for any gas smell downstream of the valve. A valve that passes gas when de-energized is faulty and must be replaced.

5. Replace gas valve if confirmed leaking

   A gas valve confirmed to pass gas when closed is a safety hazard. Replace with the manufacturer-specified valve for the model and retest the complete ignition sequence.

When to call a professional

Gas valve replacement requires licensed gas work in most jurisdictions. Do not attempt to repair or adjust a leaking gas valve — replacement is the only safe remedy. If the gas valve tests closed correctly but E275 persists, a licensed technician with a combustion analyzer and electronic leak detector is needed to isolate whether the control board or sensor wiring is producing a false signal.