Heater/Furnace Problem

[old cowboy]

Hi
I have a Terry 22' TT and the heater is not working.
The blower will come on but the burner won't fire, sometimes if I tap the contorl valve with a hammer it will fire.It is clicking but not igniting the burner. I don't think it has a pilot, its electronic ignition.
The furnace is a Atwood mod # 8520
There was a wasp nest in the exhaust, I cleaned this out but still dosn't work. Anyone know what part I need or how to fix it ?

Thanks OC

[Ray,IN]

It is likely the furnace needs a complete cleaning. I refer you to the Atwood furnace service manual
, particulary page 21 of this 58 page pdf. for accurate information. My method is to first turn off the LP cylinder valves, then remove the furnace burner assembly so unobstructed access to the combustion chamber is possible. You already know about wasp nests, spiders are attracted to the odorant in LP gas and will build nests in the chamber, hide in the actual burner nozzle or block it with a nest.
While you are in the mode, consider also cleaning the water heater assembly too.