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.
There should be a pressure relief valve that prevents any kind of dangerous levels of pressure buildup. The result is that they spill water all over the floor and make a mess but there should never be any kind of high pressure. This is really important because hot water heaters can trigger an extremely violent explosion otherwise.
Hopefully the deformation in your picture was just warping due to heat or something rather than pressure.