It sounds like the burner tube might be clogged. the propane will come out a nozzle into a brass burner tube. there is a hole in the side of the tube to allow air to be sucked in to create a flammable mixture. if the tube is clogged with a spiderweb or something else, all of the propane will not flow through the tube and some will instead escape out the hole where the air is supposed to get sucked in. Eventually it will get to the igniter causing a small explosion. try pushing a pipe cleaner through the tube until it comes out the other end, by the igniter. if that is clean, look at the igniter to make sure you see a spark between the two prongs. if not it could be out of adjustment, or it could be arcing to the gas pipe or the frame. also check the burner box for obstruction. the burner box is a tube with a piece of sheet metal separating it into a lower and upper compartment. the flame will shoot in the lower compartment, around and out the upper. if there is some blockage you may not get the correct flow to ignite. the fact that you can light with a lighter seems to rule some of this out, but still worth checking everything out. My guess is the service guy is just lighting it once and says it's ok. Maybe insist on showing them the problem if you haven't done that already. Good luck.
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