A controller for a heating cable. The heating cable includes first and second conductors and a separation layer interposed between the conductors. The conductors and the separation layer extend along the length of the cable and electrical resistance provided by the separation layer between adjacent portions of the conductors has a negative temperature coefficient. The controller includes a first switch, arranged for connecting the first and second conductors in series at one end of the cable such that if the first and second conductors are connected at the other end of the cable to respective poles of a power supply currents flow in opposite directions through adjacent portions of the conductors. The controller further includes a second switch and voltage measurement functionality. The controller is arranged to control power to the cable as a function of measured voltage across the first resistor when both switches are open.