I don't have it hooked up to a thermostat. I think I might have just had a defective pad, but I don't know. I use this brand of pads on my geckos, too, and I know lots of people who have never had problems with them. I plugged it in (not on the cage) just to see and I noticed that it would go through weird phases where it would be an okay temp, and then get really, really hot.