I'm having a problem with the flames on my Traveller, I did the recommended burn off on high for 20 minutes, I then turned it to medium to make dinner. The games went from a nice blue to yellow with just the bare minimum of blue. I took the 1 pound bottle off the next day and opened the valve to purge any gas in there. I reattached the bottle and fired it up, on high the flames were like yesterday burner on high with yellow tips. My question is what is causing this?