Zanussi DE4554S tripping the RCD

I have an 18month old Zanussi DE4554S which is causing the RCD to trip occasionally during the wash cycle (doesn’t happen every time though – once every 2 or 3 days and is always OK when on drying cycle). The water inside is always very hot when this happens. Have reset the trip, to try and allow the programme to continue – this only works when the water inside has been left to cool with the door open for about 20mins. Possibly the thermostat playing up? Any help much appreciated! 🙂