I have a payne propane furnace, model PG9MAA. It is about 15 years old. I am having symptoms that point to a dirty or defective flame sensor. All of the videos that I see online about cleaning the sensor show an easily accessible sensor. Mine is behind the burners, and there is a large pvc pipe in the way. The pipe goes to the roof of the house. I can get to the white wire connector at the base of the burner, but I can't get the unit out to clean it. Has anyone ever run into this before?

Condensing furnace? 90% or higher? Smart Valve? Those are inside a sealed box but many run on 120 VAC, not 24 VAC. Check your model online to check it out.