Lennox Furnace 8 error code
Eight flashes mean the rollout switch opened — flames or excessive heat were detected outside the normal burner area. This is a serious safety fault.
Also shown as: 8 flashes, eight flashes, fault code 8, rollout switch, flame rollout
Last updated: September 30, 2026
What causes the 8 error?
- Blocked or restricted flue venting
- Cracked heat exchanger
- Blocked burner or heat-exchanger passages
How to fix Lennox 8 — step by step
Work through these in order, from simplest and safest first. Stop as soon as the code clears.
- Do not keep resetting the furnace
Leave the furnace off. A tripped rollout switch means combustion products may be escaping where they should not.Safety warning: Flame rollout can indicate a cracked heat exchanger, which can leak carbon monoxide into the home. Make sure working CO detectors are installed. - Call a licensed technician immediately
The heat exchanger, venting, and burners must be inspected before the furnace runs again.
When to call a technician
- Immediately — do not run the furnace until it is inspected
- If you see soot, scorch marks, or smell combustion odors
Frequently asked questions
What is flame rollout?
When burner flames 'roll out' of the heat exchanger inlet instead of being drawn through it — usually because exhaust cannot exit normally.
Can I reset the rollout switch myself?
No. Manual-reset rollout switches must only be reset by a technician after the cause is found and fixed.
Sources
Every meaning and fix above was checked against official manufacturer documentation:
FixCode provides general troubleshooting information only — not professional repair advice. If you are unsure about any step, stop and call a qualified technician. Repairs done incorrectly can be dangerous and may void your warranty.