bstark wrote:

If your igniter is snapping then the igniter gap is fine and the signal is getting to the furnace to fire off but the solenoid valve to feed propane is likely not opening.

Can you get easy access to the solenoid valve itself? On my suburban, if I removed the outer panel I was looking at the fan assemblies with the solenoid valve tucked into the middle of the front of the unit so it was easy to ask my wife to perform the "switch on" job while putting a long screwdriver against that solenoid, wait until I heard the coil packs energize and give the handle of the screwdriver a light tap with a hammer et-voila solenoid opened and off she went.

Now that I had determined either a sticking solenoid valve or faulty coil packs, I removed all wires to the coil packs and tested continuity across the exposed spade lugs which were good. Now I'm thinking solenoid valve is sticking but decided to save a little effort in dismantling the solenoid and first purchase a new set of coils and sure enough, the old ones, while showing no shorts, were weak I guess. She fired right up instantly and consistantly.

Never another problem since.

On Edit the post above by Doug is right on the money AND the first thing to check with the orifice perhaps being clogged with some crud and a set of welding torch cleaning rods will give you the right size cleaning rod to gently clean that orifice with.

sundancer268 wrote:

What I found on my Suburban furnace was the fan motor would slow down when the unit warmed up and would not trip the sail switch. Removing, disassembling and oiling the motor corrected the problem. I found the problem by jumping out the sail switch and watching the furnace while the wife worked the thermostat.