a couple of things to try...
If it has been sitting for awhile with no propane
running, turn the burner on your stove on for a little bit. This clears air out of the lines and sometimes gets the far away places up and running. I had a cat heater in my old trailer that wouldn't light
no matter how I tried. Someone suggested this and it worked great.
Obviously, watch the burner flame to prevent accidents.
I also know that my furnace
in my 17 is very touchy about line voltage. The peizo lighter will fire if it is sitting at 12v, but won't if it's 11.9.
One of my tomorrow projects is to see if I can install a dedicated battery