Usually the burns are the result of the snake having to choose between being too cold or too hot. I mean a cage that has an ambient temp of like 70F and a hot rock or heat pad of 120F. They will usually choose to be too hot and get burned in the process.
To the OP, your temp on the hot side might not be what you think. If you're using a stick on type thermometer, especially. These are never accurate. A good temp gun or digital thermometer is much better.