why it stops working?

I love the rowenta iron, I buy an iron it seems almost everyother year. I use it a lot, I make quilts and use the iron often along with regular weekly ironing. It seems that the cord stops working, if I move the cord a in a circular motion it starts up again for a short time. Why is this happing? where can I have this repaired? I sent in my warrenty cards in, how do I send this iron in to be repaired while under warrenty? One iron is professional luxe inox stainless steel. model DM 800 the other is the same that model is DX8600.