Lennox Furnace 8 flashes (older boards): What It Means & How to Fix It
Compiled & reviewed by the HVAC Flash Codes editorial team · Updated 2026-06-25 · confidence: high
⛔ Stop — call a licensed pro
What does Lennox furnace 8 flashes (older boards) mean?
On older red-LED Lennox controls, 8 flashes = rollout switch open. A flame-rollout safety device has tripped, indicating flame or heat escaped the burner area (newer boards show E200). Most often caused by Blocked heat exchanger or restricted venting causing flame rollout.
What your furnace LED does. The diagnostic light blinks 8 flashes, pause, repeat — that pattern is Lennox furnace 8 flashes (older boards).
What Lennox furnace 8 flashes (older boards) means
On older red-LED Lennox controls, 8 flashes = rollout switch open. A flame-rollout safety device has tripped, indicating flame or heat escaped the burner area (newer boards show E200).
Common causes
Blocked heat exchanger or restricted venting causing flame rollout
A cracked/failed heat exchanger
Dirty burners or improper combustion
Inducer failure
Homeowner-safe steps to try
Set the thermostat to OFF and leave the furnace off
Do NOT reset repeatedly or run the furnace
Record the code and contact a professional
When to call a licensed HVAC technician
If the basic checks below don't clear the code, the fault recurs, or anything involves the gas valve, burners, flame sensor or wiring, stop and book a licensed HVAC technician. Repairs to the combustion or gas system are not DIY.
⚠️ Safety first. Gas furnaces burn fuel and produce combustion gases. If you ever smell gas (a rotten-egg or sulfur odor), hear hissing, or your carbon-monoxide alarm sounds, do not touch light switches, thermostats, or the furnace — leave the home immediately and call your gas utility's emergency line or 911 from outside. Homeowners should limit themselves to simple, safe steps: setting the thermostat, checking and replacing the air filter, confirming the furnace switch and breaker are on, keeping supply registers and return grilles open, and clearing snow, ice, or debris from outdoor vent and intake terminations. Never bypass, jumper, or reset safety switches (limit, flame-rollout, or pressure switches), never open the gas valve or burner compartment, and never attempt combustion, electrical, or control-board repairs yourself. Error codes point toward a problem but are not a substitute for proper diagnosis — when in doubt, turn the system off and call a licensed HVAC technician. Keep working carbon-monoxide detectors on every level of your home.
When to call a pro: Requires a licensed HVAC technician before running again — flame rollout and a cracked heat exchanger are serious fire and CO hazards. Do not replace or jumper the rollout switch yourself. If you smell gas or suspect CO (or a CO alarm sounds), leave immediately and call 911 or the gas utility from outside.
Lennox furnace 8 flashes (older boards) FAQ
What does Lennox furnace 8 flashes (older boards) mean?
On older red-LED Lennox controls, 8 flashes = rollout switch open. A flame-rollout safety device has tripped, indicating flame or heat escaped the burner area (newer boards show E200).
What causes Lennox furnace 8 flashes (older boards)?
Common causes: Blocked heat exchanger or restricted venting causing flame rollout; A cracked/failed heat exchanger; Dirty burners or improper combustion; Inducer failure.
Can I fix Lennox furnace 8 flashes (older boards) myself?
You can safely try: Set the thermostat to OFF and leave the furnace off; Do NOT reset repeatedly or run the furnace; Record the code and contact a professional. Requires a licensed HVAC technician before running again — flame rollout and a cracked heat exchanger are serious fire and CO hazards. Do not replace or jumper the rollout switch yourself. If you smell gas or suspect CO (or a CO alarm sounds), leave immediately and call 911 or the gas utility from outside.