Quote Originally Posted by redshepherd View Post
My 4 level rack is set up with a different heat tape square
Has the tape the same size and wattage on all the levels?

If it is try moving the probe and making sure it's well attached to the tape and possibly with some heat refracting tape to keep the temp stable.

There's always a bit of difference between levels. Extension cords are used on all professional racks and a surge protector AFTER the thermostat seems an overkill. Before is suggested tho.