How to Clean a Flame Sensor on a Lennox Elite Furnace

Shut the power off to your Lennox furnace. Do this by flipping off the breaker at the master circuit box. There should be a circuit breaker labeled "Furnace" or something similar.

Turn the furnace gas valve off and remove the front access panel. To turn off the gas valve, locate the valve on the gas line running to your furnace and turn it to the closed position.

Locate the flame sensor. It resembles a small metal pole with porcelain wrapped around it. It is typically located near the burner compartment. A clip holds it in place. Remove the clip and take the sensor out of the furnace.

Gently rub the sensor with fine emery cloth. A quick rubbing is usually all that’s needed. If you cannot see whether the sensor is dirty, hold it directly under a light. Even the thinnest film of dust or dirt appears under direct light. Replace the sensor back into the furnace.

Power on your furnace by flipping on the furnace’s circuit breaker. Turn the gas valve to the open position. If the problem was indeed a dirty flame sensor, your furnace should not experience further issues.