Fan oven trips out?

My daughters Zanussi fan oven ZDM 869X has a pecuiliar fault. The controls on the oven allow you to use it without the fan, and this is the only way it can be used, since if the fan is brought into operation, then the oven trips the earth leakage breaker after a few minutes from cold. I reasoned it must be the fan motor, but since fitting a new one, the fault remains.

Can anyone help with this?