Roll out switch tripped — possible cracked heat exchanger and CO risk.
Brand: Lennox (Also covers Armstrong Air, Aire-Flo, Ducane) | Equipment: Gas Furnace
5 flashes on a Lennox ML or EL series furnace means the flame rollout switch has tripped. This switch shuts off the furnace if flames escape the burner enclosure — a sign of dangerous combustion.
What: Crack lets combustion gases escape and pushes flames out of burner box.
How to check: Licensed tech inspection only.
Fix: Heat exchanger or furnace replacement.
Shop partsWhat: Condensate buildup blocks secondary heat exchanger.
How to check: Tech inspection.
Fix: Clean or replace.
Shop partsWhat: Birds nests, ice, dropped pipe push gases backward.
How to check: Inspect exhaust outlet.
Fix: Clear blockage.
Shop partsWhat: Poor draft causes flame disruption.
How to check: Listen at startup.
Fix: Replace inducer.
Shop partsTry our interactive symptom diagnostic tool or browse Lennox parts.