I had the same problem with an UTH. Set up just like the picture and had been checking it with a thermal gun. The readings were different even after an hour of leaving it alone. Some were reading 92 and others only 76. So I ended up ditching the UTH and I've just been using two ceramic heat emitters. One on each side and have been getting the proper Temps. I also use an acurite thermometer and hygrometer and check the Temps at least once a day with the thermal gun to make sure it's reading right.

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