I agree with sue z q that with the presser foot down you should not be able to pull thread easily through the needle, at least on the machines I'm familiar with, so that in itself is probably not an issue. And I agree with PaperPrincess that your Pfaff dealer should be able to fix the problem by getting more experienced technicians from the factory involved. Has he tried a different presser foot to be sure that it's the problem? Unless the foot has burrs that are cutting the thread, I'm having trouble understanding how the foot can be the problem.
Here's another thread from a couple of years ago that might help you -
http://www.quiltingboard.com/main-f1...m-t177903.html