Neff C1AMG84N0B/04 built-in combi microwave oven (Woosehill RG41)

Since I got this two and a half years ago, while it has worked perfectly well, it repeatedly trips the circuit breaker that it's on. This is very intermittent; on average perhaps once every week or two. Our maintenance company have sent engineers many times, and they have (speculatively) changed many components, but haven't been able to find any actual fault. Aside from that, it's in excellent condition. When the circuit breaker trips, I just reset it and switch the machine on again.