Anyone had a propane (11lb) develope a vapor lock? Last trip out my heater simply stopped working. OK, time to have it filled again. U Haul tried but said there was a bubble in it and it wont fill up and suggested I open the small valve on it to empty it. I took it home and put it in a warmer place for awhile and then it fired up again. I was a little hesitant to go out yesterday (-7 degrees) and not know if it would work. Any suggestions or solutions?