Ok if you keep getting the F21 error code then to be honest its more likely to be worn carbon brushes in the motor rather then the motor itself which is good news as a new motor is about £220.
If you are looking at fixing yourself then you need to remove the motor from the washer and at the back of the motor are the carbon brushes. Take them out and inspect them and see if they have worn down.
But if you don't want to go messing with it yourself then if getting someone in to replace the carbons you are looking at about £70-80 for the repair so a lot cheaper then a motor.
If you need anymore info just get back to me.