My Thermacell experience;
I bought a Thermacell a couple years ago and tried to use it around 8,000 ft in NM, I hiked into an area and the Mosquito's were swarming, so I whipped out my new Thermacell and after about 10 minutes of trying to light it I had to give up and put on my rain suit because I was getting eaten alive once suited up I went back to the Thermacell and tried for another 10 or 15 minutes but all I could get was a glow for a few seconds and it would go out, I tried changing fuel canisters and everything else I could think of and ended up putting it away. I woke up the next morning and thought WTH so even though the Mosquitos were not out yet I tried it again and to my surprise it lit so I let it burn for a little while and then put it away, that evening I stopped to make camp and broke out the Thermacell, 30 minutes later I still couldn't get it to light, the next morning the dam thing lit right up! I don't know if it was temperature or elevation or a combo of both but I returned the thing.