Why does my 4 year old De Deitrich hob only work intermittently?

My De Dietrich induction hob works only intermittently and unpredictably. There is no pattern to it. Sometimes it does, sometimes it doesn't. What is the matter with the thing, can it be fixed and even if it can, is it worth it? The elements have already been replaced - only 2 years ago! In between it has very light usage.