Pfaff 1222 frozen 20 mins after I start using it

Question

Every time I use my pfaff it freezes after 20 minutes sewing..  I cannot move the  right hand wheel forward, only backwards which makes the machine foot go up and down very fast.  I have had my machine repaired several times. I am always told that there is a different problem. I love sewing but I fear I may have bought a lemon.  It is very frustrating. Just when I am whizzing along enjoying myself the machine stops.  I am considering buying a new machine which is not a pfaff because I am so tired of this ongoing problem.Can you help me please! Di from Australia