Bosch Exxcel 1400 Express-trips power RCD after 20mins any cause/fix? ?

After some 20 minutes into wash cycle the m/c trips the RCD. I've checked the blantantly obvious of the plug, mains cable and any internal chaffing to all visible wiring but can't see any apparent cause. Does anyone know if there's a recognised fault within the programme switches or any other reason other than a timed 'go buy a new one bug' set by Bosch! Its about 3 years old but in great nick compared to my previous machine and so can't see any reason. Many thanks.