Oxidized Furnace Flame Sensor 
Sanded Furnace Flame Sensor
- Year Repaired: 2020 – Present
- Symptoms: Furnace pilot light turning on but not heating
- Cause: Oxidized flame sensor
- Outcome: Sanded off oxide layer
- Material Cost: $5
- Time: 30 min
Notes
This is a very common problem with all furnaces and boilers. It was a very straightforward repair. There were a couple possible issues, but since the sensor was visibly dirty this was the first one I tested.
The Handyman Dan London 