E434
Lennox
Repeated Ignition Failure Lockout
Thermostat shows E434; furnace may lock out after several failed ignition attempts.
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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 burners on Lennox furnace, Misaligned flame sensor or ignitor, Intermittent gas valve operation, Improper combustion air or venting issues
How to Fix / Troubleshooting
Safety: Turn off power and gas before servicing burners.
- 1. Inspect burners: Remove the burner compartment door and visually inspect burners for rust, debris, or misalignment. Do not bend or drill burner ports.
- 2. Clean flame sensor: Remove and clean the flame sensor with fine steel wool as described in other steps.
- 3. Check venting: Ensure intake and exhaust vents are clear and properly supported. Correct any obvious sags or disconnections.
- 4. Reset lockout: Restore power and gas, then reset the furnace by cycling power. Observe at least three ignition cycles.
If E434 returns, professional combustion and gas valve diagnostics are required.
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Repair Difficulty
Hard
4/5
Required Part
Burner Assembly
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