Probably air in the lines.
Here's how I do it. Use a BBQ lighter.
Reset the system. Turn off the fridge. Turn off the propane tanks, hold the lit lighter over the stove burner and turn on the burner. Let it run until no more propane or air comes out of the line. This reduces the pressure on the "leak protection valve" in the propane tanks.
Disconnect the propane lines from each tank. Wait about a minute or two and reconnect them.
Make sure all propane appliances are OFF. Stove, fridge, furnace, hot water heater.
SLOWLY open one valve on a tank. If you hear a SNAP, then it was too fast and the leak protection engaged and shut off the flow. The valve should be opened completely. Repeat if you have a second tank.
Go inside and use lit BBQ lighter over a burner and turn that burner on high. Don't let the air blow out the flame. When the air is purged, the propane burner will light. Leave it run and turn on all the stove burners and let them run about 20-30 seconds. Turn off burners.
NOW you can turn on fridge, make sure it lights. (you can hear a low roar near the outside fridge vent when running on gas)
NOW you can turn on the furnace. It may blow up to...maybe a minute(?) as it purges air from the line and gets happy with the safety sail switch and such. Then you'll hear it light.
I believe it is quite likely that you had air in the lines, or propane not flowing (leak detector valve closed?). The fridge and furnace have safety devices that can be troublesome if they repeatedly fail to light (as air is purged from the lines).
Lighting the stove burners first, each time the tanks have been off or disconnected, seems to be 100% reliable way to avoid such troubles.
You shouldn't need to reset the system each time, just purge the air after the tanks have been off or changed. But since you are having trouble, it is best to do the full procedure to test your furnace.
Hope this helps! Let us know how you make out ;)
(Hope this message gets posted. Stupid Captcha all over this site :G )
