Lennox Code 33
Furnace Ignition Failure
What Lennox Code 33 Means
Furnace Ignition Failure – Furnace will not ignite or flame goes out immediately
Common Causes
- Ignitor element burned out or cracked
- Flame sensor dirty or defective
- Gas supply blocked
- Ignitor wiring loose
- Control board failure
First-Check: Step-by-Step Troubleshooting
- Check ignitor for visible cracks or burns
- Clean flame sensor with soft brush
- Verify gas valve open
- Test ignitor continuity with multimeter
- Inspect all ignitor wiring connections
- Replace ignitor if resistance out of range
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