Sounds like the heating element.
Just guessing, is it a CTD40 ?
If it is the element will be serial number specific, that is, depending on what the serial number is, you'll need one of a choice of two to replace it. Look on the plate.
Each one is about £45 to £55 to replace.
If you get a technician to replace it, then add about £60+ to that for his/her work.
Hope that helps.
c2001
October 2009