What is the Flame Sensor
The flame sensor senses the flame to ensure the furnace has fired. If there is a gas valve open but the furnace hasn’t fired, it doesn’t emit raw natural gas or propane.
DIY Flame Sensor Diagnosis
Here is a step-by-step furnace flame sensor diagnosis guide.
1. Turn off electrical power to your furnace either at the furnace or at the electrical box.
2. Close the gas valve.
3. Remove the flame sensor mounting screw.
4. Gently pull out the flame sensor.
5. Visually inspect it.
6. If the sensor insulation is intact but looks burnt or has a small amount of corrosion on it, the sensor might simply need cleaning. The best way to clean it is by using a dollar bill.
7. If the porcelain insulation is cracked, or if cleaning doesn’t fix the issue, the sensor must be replaced.
8. After cleaning or replacing the flame sensor, remount it
9. Turn the power on, open the gas valve and light the furnace
Also… watch the video to see it demonstrated.