I can't believe I didn't catch this before, but are you talking about the ZooMed HygroTherm?
The reason I ask is that I really don't think that's the best Tstat for controlling a UTH. Don't get me wrong, it's a great controller, and I use one myself, but the size of the probe coupled with the fact that it can't be used directly on the bottom of the cage (inside or out) means it's really best for ambient air temp.
If you're using something else, just disregard all of that.
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