Can I fix my Neff double oven fan assisted U 1442?

The oven, grills etc all work perfectly, but when you turn off whatever you have been using, oven, grill or whatever, the cooling fan stays on all the time. Think it usually goes off after 20 minutes or so, when the appliance gets cold. I have tried turning it off at the mains for a couple of days, but the cooling fan came on again as soon as I turned the power back on, even though it had obviously been cold for 2 days.