I'd hate to see your enclosure on a cold day!!!
Tell me though - what does the 'reset' button do?
Does it fix your problem?
Best thermometers for reptile enclosures are probably alcohol filled glass thermometers - or at least something that can be calibrated!
We used to calibrate our electronic ones (which had calibrate buttons) by using a bucket of ice sludge and setting to 0'C. It usually worked very well.
If the reset button works, and you want to test it's correct, that is the best way to do it.