Gary,
I have the same problem, Ive got to say not impressed with the quality of this item.
As far as I can see its associated with the cooling flap which opens when you use the appliance as a microwave.
If you look at the light inside the oven when you start the microwave the flap should open in around 30secs if it doesnt then the oven comes up with E14. If you take the cover off you will see the flap (top right front) is operated by a stepper motor turning a cam which activates a microswitch. If the motor or the microswitch is failing you will get the error E14. When you turn the oven on from the mains the motor turns the cam rotates then stops when the microswitch operates.
I tried to get around the issue as I only use oven as microwave by overriding the switch but this will fail because the contoller circuit will check the flap open and closed position.
In my case I think its the motor, they are about a £100 to buy.
I have checked the microswitch with a DVM looks good and 240v is applied to the motor but it sticks intermittently.
I would buy a new motor but the turntable is intermittent and the front cover is water marked between the 2 pieces of glass.
I have taken the motor apart, it has a number of plastic reduction gears inside to which I have applied a very light gease. Putting it all back together it appears to be working!!!
If it fails again I'll throw it in the skip and buy a new one NOT AEG.
Hope this was of some use.
Regards.
Pete Burfitt
March 2008