Twice this week we have gone out in the heat (hot car, hot outside, etc) and both times J has started going up, up, up. I changed his infusion set the first time, thinking it was what was wrong. Nothing. When I finally changes his insulin, he started coming down. Same thing today - he was in the 300's for HOURS. I changed his set twice. First time because he hit 300 and he was due for a change today. Second time because the first site pulled out. Nothing helped, until I changed the cartridge of insulin. Do you think it's more likely that the insulin is going bad in the heat (those little cartridges can heat up quickly, I'm sure) or maybe air in the tubing? I just can't figure out it. I did see some air in the tubing when I primed it but not much. It just seems to be the heat.