How do you heat them up? It would be impossible to overheat if you thaw the pinks in warm water or leave out at room temp. Heating in a microwave or oven (?) isn't recommended as you can cook the mouse. If the mouse is overheated then, generally, a snake would refuse it. They like them to be at body temp so that they can 'think' the mouse is alive, by instict, a snake would chose not to eat something obviously dead.
So if you are thawing your pinks by any means that could overheat them, stop and try the methods I mentioned earlier. I'm sure others have diff. methods to suggest....