The thermal overload “jammed”, so the heaters never stopped heating. The pressure release valve operated and made a fucking mess. I was away when it happend. When I came back, as soonas i opened my house door it felt like a jungle in there … warm and damp air Could have been worse. The pressure went up so high that the top cover warped.

Thanks! But that is far from being intuitive. I get it that once you know, you know… but still…!