Smeg Opera A2 Range cooker fault?

The main oven on our Opera A2 range cooker trips the main circuit breaker on our fuseboard. Turn it on fan oven at 175 degrees and leave it for around 4 minutes to heat up, the fan kicks in ok, the oven starts to warm up to around 120 degrees and then click the RCB trips. All other functions are working ok.
I have swapped the overheat statin case it was that
Any ideas.