Only thing I can think of off the top of my head is making sure there is a good seal with the lid. A lot of members here crack the lid at the end of cooking chicken to crisp up the skin. I have noticed with mine that there are times where I need to really press down on the lid to make sure there is a good seal.
If that isn't the issue, I would call Pit Barrel, although I never had any issues, they are always available and willing to help.