Had the same issue. In my case the Heater relay on the control PC had failed. If you can use a soldering iron you can change just the relay. New relay from maplins £2.99 ( 12V DC 20A SPDT Relay) you need to cut off the normally closed pins . Otherwise its a controller assy £70.00.
Relay is in front of the Heater socket that takes the cables to the heater assy. If you have no mains Voltage at the heater, then its likely to be the relay.
Bob Watson, January 2017