Lennox Furnace E275 Error Code — What It Means
E275 on a Lennox furnace indicates a soft lockout caused by flame sensed out of sequence. The control detected flame when it should not have been present, then the flame signal disappeared. The furnace responds by shutting off gas and entering a 1-hour soft lockout period. The lockout clears only when flame has been proven stable again.
This is a flame-proving and ignition-sequence fault. The control expects flame to appear only during commanded ignition, so detecting flame at the wrong time or losing it unexpectedly signals a serious problem, most commonly a gas valve that is leaking by or not fully closing.
Common Causes
- Gas valve leaking by The valve does not fully close, allowing gas to be present when the control is not commanding flame, triggering the out-of-sequence detection.
- Flame sensor feedback issues A false flame signal or unstable flame signal causes the control to see flame when none exists or lose the signal unexpectedly.
- Ignition or flame-proving sequence problems Improper burner ignition or flame failing to stabilize during startup can result in the control detecting flame inconsistency.
- Control board or wiring faults Problems in the flame-sense input circuit or gas-valve output wiring can cause erratic flame detection or valve control, especially if the code repeats.
Step-by-Step Fix
- Verify the E275 code on the furnace display or error recall to confirm you are troubleshooting the correct fault and not a different flame-related error.
- Inspect the burner compartment for any unwanted flame presence or signs that gas is present when the furnace is not calling for heat.
- Check for a gas valve leak by examining the valve for bypass or failure to close fully, since Lennox directs you to check for gas valve leaks when diagnosing E275.
- Verify proper gas flow and ignition sequence to confirm the ignitor lights the burner only when commanded and that flame appears on schedule.
- Inspect the flame sensor circuit and confirm the sensor rod is clean and positioned correctly so the control can prove stable flame after ignition.
- Allow the 1-hour soft lockout to expire or restore correct operation and then confirm the code clears when stable flame is established and maintained.
- Test or replace suspect components if the problem recurs, focusing on the gas valve first, then the flame sensor, and finally the control board and wiring in the flame-sense and gas-valve circuits.
Parts Often Needed
| Part | Notes |
|---|---|
| Gas valve | Amazon | Primary suspect when E275 appears. Replace if the valve is leaking by or not closing fully. |
| Flame sensor | Amazon | Replace if the sensor rod is fouled beyond cleaning or the flame-sense circuit signal is unstable. |
| Control board | Amazon | Consider replacement if flame sensing or gas-valve control is abnormal after verifying the valve and sensor are good. |
When to Call a Pro
Call a qualified HVAC technician for E275 if you are not trained in gas appliance service. This code involves flame sensing and gas valve operation, both of which require proper test equipment and knowledge of combustion safety. A leaking gas valve or faulty flame sensor can create unsafe conditions. A technician will perform leak checks, measure flame signal, verify ignition sequence, and replace the gas valve or other components as needed. If the code repeats after initial repair or if you smell gas at any time, shut off the gas supply and call for service immediately.