It was the probe that came with the DC controller, the problem was it seemed to be very inaccurate in sensing the temperature so it became a 'worry'. Couldn't be bothered to pfaff about so bought the DC in line and sensor. The old rad probe on my DC controller just unplugged and the new sensor plugged straight in. It seems as though it was designed for the probes to be changed and/or replaced if faulty. We'll done Aussie designers!
Another upside with the DC in line joiner is it now has two NPT holes, one for the probe and the other can be plugged (comes in kit) or you can buy an air vent to get rid of pesky air locks. Unfortunately T7 don't at the moment sell the vents but I've advised them and they are looking to get them from DC.