I have found this fault on most bosch and even Aeg dishwashers. I simply open the control module and clean it. Second step is to identify the weak solder joints on the module which is always on the heating relay. By using a solder sucker I remove the old solder joint and then using a solder iron I neatly resolder it. Takes no longer than an hour and the customers is more then happy as u saved them time and money.