Herpstat is a great product, i have never had issues with mine. If anything is wrong with it i would chalk it up to user error or buying a mistreated used unit. If i were the OP i would keep reading over the user manual and double check every connection and probe. Make sure if you have two different probes that they are hooked into the correct spot on the back of the unit and not switched. Also make sure that your heat tape isnt the issue too, check for all possibilities.