Hello; I have a LP Empire Wall Furnace model # FAW-55 SPP in my garage (hooked to a 20lb tank-full). I turn on the gas & ignite the pilot light. After a few seconds the pilot will stay on by itself as it is suppose to. I then turn the control on the furnace to "On" & the thermostat is set to at least 75 degrees. But the burners never light. Last year the furnace worked fine for the few times I used it. Now, zippo! I took the front cover off, used compressed air (nothing outrageous) on the burners but, nothing helped. Any clues what might be the problem? Thanks