BDW13 Tripping main house circuit breaker?

Strange one this. The main house circuit breaker has been tripping. Eventually I found it was the dishwasher causing the fault. The dishwasher seems to work fine for at least 30mins before it trips the breaker. I thought it must be the element, but then thought that the element must be used earlier in the cycle. I use the normal program, which does include 2 pre-rinse cycles (according to the manual). The rinse cycle program works fine so again pointing to the element. Has anyone seen this fault? I guess I should be testing the element for a short circuit, any advice?