give us a little more information about what we're talking about make, model, year? there should be a thermostat somewhere that controls the heater. if the thermostat is not telling the heater to turn on, there won't have a spark
Did you try lighting the stove to see if you're getting LP flow? Maybe you turned the LP tank valve on too quickly. Try turning it off, waiting a few minutes, then turn it back on slowly and try your furnace again. Does your thermostat have a battery? Does it have a good charge?
I have a 2004 Flagstaff pop up and mine looks pretty much the same. if your thermostat is working properly it should do two things once the thermostat is raised up: turn on your blower then start a time sequence for the igniter the starting igniting. sounds it as is the thermostat may not be working..