Georges posts are correct. I would also like to add that aluminum tape can throw things off for a couple of reasons. First aluminum transfers temperature quickly. Thats why we use it for our probe. Aluminum tape is transfering temps from a wide area. Which means when the heat tape turns on it can heat up the probe very quickly but the actual tubs remain cold as the thermostat shuts off power. On the other side of things, when your room cools it also transfers this quickly to the probe including every little draft. So you can get some mixed results. Plus of course aluminum can conduct electricity which is no good sitting on top of a what is technically a bunch of wires running 120 AC. If the heat tape ever gives up (and it happens more than you think) you could double your safety hazard with that tape. I would just use packing tape if necessary but also I would put the probe either in a tub over the hot spot or taped to the back of the tub over the hot spot but not directly on the heat device.

If after you have that setup and the temps are not making it to your set temperature then the issue is the heating device is not enough. You can either add more heat tape, change to a higher wattage or larger size heat tape, or increase the ambient room temperature. Setting the temp higher on the thermostat will not make the difference unless its getting within 1 degree of the target temp and its dimming the voltage but for that you can try out the different power matching modes on the Herpstat.

Hope that helps!

Dion Brewington
Owner, Spyder Robotics