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CRITICAL URGENCY

Lennox 5 Flashes — Roll Out Switch Open (SAFETY)

5 flashes

Roll out switch tripped — possible cracked heat exchanger and CO risk.

Brand: Lennox (Also covers Armstrong Air, Aire-Flo, Ducane)  |  Equipment: Gas Furnace

SAFETY: One of the most serious furnace codes. Cracked heat exchanger releases carbon monoxide into your home. CO is colorless and odorless. If anyone has headache, dizziness, or nausea, evacuate and call 911.

What This Code Means

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.

Likely Causes (Ranked)

Common and serious

Cracked heat exchanger

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.

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Common on 90%+ AFUE

Plugged secondary heat exchanger

What: Condensate buildup blocks secondary heat exchanger.

How to check: Tech inspection.

Fix: Clean or replace.

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Common

Blocked flue/exhaust

What: Birds nests, ice, dropped pipe push gases backward.

How to check: Inspect exhaust outlet.

Fix: Clear blockage.

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Possible

Failed inducer

What: Poor draft causes flame disruption.

How to check: Listen at startup.

Fix: Replace inducer.

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Diagnostic Steps

  1. STOP — do not keep resetting
  2. Shut off gas at furnace
  3. Verify CO detector working
  4. Call licensed HVAC tech

Frequently Asked Questions

Can I keep resetting the rollout switch?
No. Resetting without addressing the cause risks CO exposure.
Cost to repair?
Heat exchanger $500-1200 labor (part often warrantied). Often cheaper to replace furnace.
Same on Armstrong/Ducane?
Yes — Lennox family identical.

Related Lennox Codes

Lennox Error Code 4 FlashesLennox Error Code 3 Flashes

Related Symptoms

Furnace Smells GasFurnace Pilot Yellow FlameFurnace Keeps Shutting Off

Need More Help?

Try our interactive symptom diagnostic tool or browse Lennox parts.

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