I finally experienced this issue and confirmed that the control will not allow heating if it is reading the temp sensor out of range. I was sort of hoping the program was written to where it would know it was at least low-out of range and would turn the heat on to bring it into range but I found that the software was written to where when it is out of range, it does not know what is going on and will not allow any functionality. I simply applied 5 sec of heat from a propane torch, it started showing temp on the control panel, and we are off. NOTICE, once you are showing temp, you MUST turn the unit off, then back on to reset it.
The outdoor temp here is only in the 20s so I am surprised it will not dip that low but thermocouples are usually tuned for a certain range and it is probably set up to have a high level of accuracy only at cooking temps. It any case, it did not ruin my cook and I would not return it for this problem. It would be nice however, if it would just kick the heat on to warm the box and bring the temp into range.