Atwood hydro flame furnace problem

[Kevin and Beth]

My pinnacle came with an atwood furnace. I had a problem last year with the reset switch on top of the furnace. It was not resetting properly, and in pulled the furnace out and replaced the switch. It was fine last fall, but this spring with the cooler weather we have used the furnace a lot and it is tripping this switch every time it is used now. I can take the basement wall down and reach the switch to reset, but to replace I'll have to pill the furnace out again. Anyone have an experience troubleshooting these furnaces? It's 5 years old now I'd really like to get whatever is wrong figured out.

Thanks