Hiya,
There isn't a lot you can do to narrow the fault down without having test equipement and the ability/knowledge to use it.
To find the fault would require the use of a megger. (test equipment).
Do you have and can you use a multimeter and a megger?
Unplug the appliance and take the inspection panel below the door off.
Check to see if the base has water in it.
If it has, use a sponge to remove the water.
Allow the machine to dry and try it again.
If there is no water then it's possible that the heater has gone faulty and is causing the fusebox to trip.
Check for the water in the base first.
Hope this is of some help.
Let me know how it goes or if you need more help.
Thanks
Home Appliance Technician
Whitegoods engineer working for a multibranded national company in the UK.
Heaters on the Bosch machines cost around the £80 to £100 mark.
Good luck with it, see if you can find one of the free call out people and get a quote off them.
Then compare it with a price from Domestic and General for a repair and 1 year extended warranty on the whole appliance. www.domgen.com will get you details and the phone number.
good luck.