If the furnace doesn’t light it will try three times and then fault. To clear the fault you have to reset the furnace either by turning it off and back on at its master switch behind the outside panels or turn the 12 volt
power off and back on with the USE/STORE switch.
When the furnace tries to light, it does the following:
1. Turns on fan
2. Runs fan for a while to clear any unburned propane from the combustion chamber
3. Turns on the propane. You should hear a click and you might be able to smell propane in the outside exhaust
4. Sparks to light the propane
5. Senses the propane burning and continues running until the thermostat says to turn off or,
6. If not sensing burning shuts off and retries the process two more times.
Where in the process it stops is a clue as to what is wrong.