Rack temp

Who was the maker of the rack system? Most come with instructions on the best way to attach a thermostat's probe.

I messed around with my probe placement on my boaphile rack, and was unhappy until I followed their directions.. lol.

What is your room temperature?

I ask because here in MN, our indoor temps are about 65 in winter. This is much too cold for back-heated racks, and we absolutely rely on belly heat to provide warm hides and adequate hot spots. Back-heated racks are wonderful, but they work best if they only have to raise temps ~10-12 degrees or so.

I will have to agree with everyone else. Some 3" belly heat might be a better option. How much heat tape are you running through this thermostat? My guess is that your thermostat cannot keep up with the amount of heat tape you're using or you have a faulty thermostat. I recently learned all too well what can happen when your thermostats take a dump on ya.