hi
we have the same problem and have found out its the heater cut out sensors which fit just above the heating element at the back behind the small raised panel. You can get them in kits from www.sparesrus.co.uk at 15 pounds 95p which is a lot cheaper than having to have an engineer look at it. You will need to remove the part to see what colour dot one has as the parts are colour coded.
andy, June 2004