Heating pad problems

[JRLongton]

sorry it's a bit hard for me to describe what the problem is. To simplify everything, the heating pad is just heating it to random temperatures. I cannot control it with the thermostat because it will just do whatever.

What do you mean "random temperatures" and "will do whatever"? From your first post I read that you set the stat at 96, got a temp too high, dialed it down and got to 87F, which should be just fine. Are you sometimes getting much lower temps? How much lower?

The only possible thing I can think of is that the thermostat turning the heating pad off is making the tank cool down quicker than it's being heated.

Which raises the real question. What is the ambient temp of the room? The direct heat of the UTH against the stat probe will read high enough to turn off the UTH, but if the room is too cold, the heat will dissipate through the material and substrate before reaching the surface where you're measuring it.