Rule out the heat tape and the probe. Get a light bulb and something like a clip on socket or even a regular lamp and use that to test the functionality of the helix. Should be able to test the proportional functionality of the system with the bulb by moving the probe back and forth with the bulb. If it is working it should brighten the bulb as you move it away and dim it as it gets closer. Barring error codes it could be anything from a faulty probe to something with the heat tape to a defective system that isn't throwing errors. Might even be able to test the temp of the light bulb but not sure how accurate that would be with a temp gun.
I would think that a simple light test should be able to at least see if the probe is working to send signal to the unit.