E355
Lennox
Flame Sense / Flame Signal Error (communicating report)
Thermostat shows E355; furnace may short-cycle or not complete a heating call.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Dirty flame sensor rod, Poor burner ground to Lennox furnace chassis, Low gas pressure causing weak flame, Faulty flame sensor circuit on control board
How to Fix / Troubleshooting
Safety: Turn off gas and electrical power before servicing burners or flame sensor.
- 1. Access flame sensor: Remove the burner compartment door. Locate the flame sensor (a small metal rod in front of a burner, connected by a single wire).
- 2. Clean sensor: Gently remove the sensor and clean the rod with fine steel wool or a Scotch-Brite pad until shiny. Do not use sandpaper that leaves deep scratches. Wipe with a clean dry cloth.
- 3. Check ground: Ensure the burner assembly and control board ground wire are tightly fastened to the Lennox furnace chassis.
- 4. Reinstall and test: Reinstall the sensor, restore power and gas, and run a heat cycle. Observe if the furnace stays lit.
If E355 persists, the control board or gas supply may need professional evaluation.
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Repair Difficulty
Medium
3/5
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