It will most likely be a thermostat that has gone.
They come as a kit and both need replacing. They are located above the heater element which is behind the cover at the rear of the machine. Just a simple matter of removing about a dozen screws.
You can purchase the stat kit from us here - just copy and paste in to your browser the following link:
These are the ones for your model, even though its not listed.
http://www.ukapplianceparts.com/laundry_models.asp?search_fd3=Thermostat%20Kits&search_fd17=t620
Lee, January 2007