When the thermostat calls for heat, the blower turns on for about 25 seconds after which ignition is attempted. If the blower doesn't get up to at least 75% of full speed, ignition is not attempted. After 3 failed attempts at ignition, the furnace shuts down and is in a safety lockout until the thermostat is recycled.
Check your propane at the range to purge air from the lines and ensure you have propane flowing. Close the valves on your propane tanks and re-open them verrry slowly so as to not trip the overflow protection device inside the tank.