indesit double oven FDE20 when turning the fan assisted oven on to pre-heat the fan does not kick in so oven gets to hot and trips at main distribution board, we have to go through this process of turning off and back on about 3 times before fan actually kicks in and then the oven works as it should.Could this be a problem with the fan or thermostat,the single oven above works fine. Any advice or guidance would be really appreciated