Could also be the thermostat cut outs above the heating element, these come in packs of two for about £13. They can be found by removing the bar and 2 smaller panels at rear. They are white discs with two connectors either side, (one disc has a green dot). With the plug out gently feel the underside of the discs and if one or both are concave then they are blown. If they are okay then there is a third one at top of the front door opening. Touch them gently as too much pressure can push them in.
Ian B
February 2007