Ok so a couple things here:
It is highly suggested to sandwich the thermostat probe between the UTH and the glass, so the probe is on the outside of the tank. Leaving it inside, your snake can move it, pee on it, and generally just mess with it in ways that can lead to a dramatic temo spike =burns. Use a temp gun to determine temp AT GLASS (not on top of substrate) so you can determine best temperature to keep thermostat on. Will be a slightly higher setting than temp you are looking to get, that is normal.
A 40 gallon is really not gonna last very long for a burm, especially if it's already 4 ft. Also, a burm can very easily get out of those sliding mesh tops if you're not careful (and even if you are). Suggesting a cage upgrade here.
As far as why he didn't eat, it is definitely possible that it is because he is in shed and will poop with the shed and leave you a nice package. But would strongly push you to not put your snake in a position where he can be injured by live rats. Whatever that looks like to you as far as changes.
Can you post pics of your setup? We would love to keep helping with suggestions to give your snake a comfortable, healthy, and stress free life!
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