OEM Lennox Flame Rollout Limit Switch — 47K18

The genuine OEM Lennox 47K18 flame rollout switch is a manual-reset safety limit that protects your Lennox furnace from dangerous flame rollout conditions. Mounted near the burner assembly, it senses excessive heat that occurs when flames roll out of the burner box — typically caused by a blocked or cracked heat exchanger, restricted flue, or poor combustion airflow. When it trips, it immediately cuts power to the gas valve to shut the furnace down and prevent fire hazards or carbon monoxide exposure.

Symptoms of a tripped or failed rollout switch include a furnace that ignites briefly then shuts off, no heat with the switch button popped out, or repeated lockouts. A switch that has tripped should never simply be reset without diagnosing the underlying cause, as it indicates a genuine combustion or venting problem.

Because this is a life-safety component, OEM matters. The Lennox 47K18 is calibrated to a precise temperature trip point matched to your furnace's design and mounting location. Substituting a generic switch with a different setpoint can allow unsafe operation or cause nuisance trips. Always replace with the factory-specified part and have a qualified technician confirm the furnace is safe to operate.