I think that maybe it's possible that you have a leak in the line. I'm not positive because I'm not there to witness it. But I think when you turn on the gas and it says lit for a while after you turn it off there could still be gas trying to get through and it comes out of the line. Try calling a gas company they could tell you what it is. I'm only 15 but willing to help. Check your line for any air that might be comming out.