How can I fix my Neff B6784 N0GB/01 combination microwave/fan oven?

This pyrolytic cleaning combination microwave and fan oven is just over 2 years old! My elderly Mum noticed circuit-breaker tripped 2-3 secs after microwave function was started. After re-setting, microwave function still cuts out consistently after 2-3 secs although CB no longer pops out. Rest of oven is fully functional. Rumour has it that this is a known problem but has anyone got a clue? Can't get any advice from Neff and estimates for 'repair' and 'parts costs' are therefore very open-ended for my Mum. I am technically competent so tech answer would be OK.