First to Euphoria, Thanks for the update for the thermostat. I recently researched getting one since the one I have runs the furnace over the set temp by at least 5-6 degrees and then drops back some before coming on. I got to use it a couple weeks ago for the first time for real when it dropped down to 19 outside. My question is, does the digital run down the battery when it is not being used...display, etc. ? I am not sure I am ready to break into all the wiring, but had considered a digital thermostat just for the furnace.
For jimrex, I would have had to take my furnace to the local Camping World place for professional troubleshooting if it had been a gas valve or solenoid that was bad. Fortunately I found the problem and it was easy for me to fix. Good luck with your unit. The "sail switch" has to close before it will release gas, but I suspect it also releases the gas just before the spark goes off for the ignitor, so I would strongly suspect a gas valve. Do you get gas to your stove ? If not, it might be the regulator at the tanks. It helps to run the stove and makes sure there is gas in the lines over to where the furnace is before you start the furnace.