The probe has nothing to do with what is happening. The simple fact is, the temp where you are measuring (digital thermometer on back wall of center tub) isn't getting much higher than 80 deg. Period. Racks that use back wall heat are best for rooms which are already heated to the high 70's (if keeping exotics in the racks like boas/pythons.) If keeping colubrids you may be fine. You can increase the temp by placing a sheet of polystyrene foam (Home Depot) over the front of the rack. Make sure you use your thermostat then.