Bosche Exxcel Auto Option not heating water?

It seems that over the last week or so I have noticed that my dishwasher doesn't seem to be heating up the water, so I'm dishwashing in cold water! At the moment I have to pre-wash everything in the sink before I load the Dishwasher - Not really the point of the thing ...or that water efficient!
Can anyone tell me if this is a case of having to change the heating element, and if so is that an expensive job and is it something a plumber would do if I get the part?
Mike