When the wall furnace lites it produces a bang and some fire around the propane entrance. I suspect when the thermolpile was replaced at the service dept. that the orofice was misaligned and is causing turbulance at the propane entrance to the burner. It does this intermitently and is alarming. This is a Empire Model GW-25-5(SG,RB) or GW-35-5(SG,RB) Propane