Machine tension k**b does not work.

Question

Been having this problem since I received the machine. I hope its just something I've done wrong and can be fixed easily. It seems I can never get the tension to work properly. It is either completely loose or very tight. It rarely works enough to become tight though. When I sew, most of the time the top thread will loop under the lower bobbin until the thread breaks. This is when I have the tension set between 3 and 5.