There may be separate heating elements for the fan oven function and the conventional oiven function.
If that's right for your oven and the fan oven element has failed, you will pretty much have th esymptoms as you seem to say (I'm a bit worried about interpreting from your English, though).
It'll be easy enough for your electrician friend to check the element and shouldn't be too much for a spare. Try www.espares.co.uk
X, March 2015