How to Clean a Lennox Flame Sensor

The flame sensor in your furnace is designed to ensure that the flame ignites. This keeps the furnace from leaking gas into your home if there is an ignition problem. Oftentimes the flame sensor will get dirty or coated. This happens because of the sensor being exposed to the flame. If this sensor doesn't register the flame, your furnace will shut down. However, cleaning a sensor is a simple solution to try prior to calling an expensive repair person.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• Screwdriver
• Fine grit sandpaper

1. Turn off the furnace. A properly installed furnace will have a dedicated power switch nearby. This will look like a light switch.

2. Remove the furnace door using a screwdriver. The door will lift up and out to give you access to the internal parts of the furnace.

3. Use a screwdriver to remove the flame sensor. The sensor is a thin, metal rod that will be in the path of the burners. You should be able to free it with one screw from below the burners.

4. Use sandpaper to clean the entire sensor. The sensor will often have a greenish coating if it is too dirty.

5. Reinstall the sensor and turn the power back on to the furnace. With the door still off push the safety switch located at the front of the furnace, inside the door cavity. It will be a black switch that would be depressed if the door were in place.

6. Hold the switch while the blower and burners start up. If the sensor is still dirty, the furnace will shut off after a couple of minutes.

Tips & Warnings

• Sensor problems can be diagnosed fairly quickly. If the burners light and the furnace goes out after that, it is probably the sensor.
• Problems related to burner ignition or gas issues are best handled by professionals.

References

• Heating Problem Diagnosis Site