Furnace cycles on and off; LED flashes 5 times repeatedly on Armstrong Air control board.

Critical Safety Warning: A 5-flash code can indicate unsafe combustion or flame rollout. Turn off power and gas to the furnace immediately. Do not operate the furnace until it has been inspected by a qualified HVAC technician.

Homeowner checks (visual only):

• Inspect around burner compartment: Look for signs of scorching, melted wiring, or soot around the burner and rollout switch area. If present, do not attempt further operation.
• Check flame rollout switches: Some Armstrong Air furnaces have manual-reset rollout switches near the burners. If tripped, they may have a small reset button. Only reset once after confirming there is no visible blockage or damage. If it trips again, call a technician.
• Do NOT bypass safety switches: Never jumper or bypass rollout or limit switches. They protect against fire and carbon monoxide hazards.

Professional-level checks (for technicians):

• Verify gas valve is not leaking when de-energized.
• Inspect heat exchanger for cracks or blockages.
• Check venting for severe restriction or backdrafting.
• Test flame sensor wiring and control board flame circuit.