Bosch washing machine tripping fuse box

Hello Tim. It sounds like a possible heater element problem. The heating element should kick in after a couple of minutes. However, to test whether it is that you need a specialist installation test metre that engineers use. Without one you would have no option but to just replace the heating element and hope that it fixes it. It's risky taking the element out to inspect it, which may or may not show any fault because the way that heating elements are fitted makes it very difficult and sometimes impossible to refit them once removed. These two articles should be read for further information -

Removing the heating element from the washing machine

Washer tripping electrics