Immersion heater has water in the cap

[Ricktee]

My immersion heater tripped the mains breaker, when I took the cap off it was full of water and the element seems to be shorted to earth. It's been there for a while so ok I need a new one but how is the water getting into the cap. I cleaned it up and left the cap off check next day full of water again, can't see where it's coming from. Any ideas?

 

[snowhead]

It's either coming in through a leak in the thermostat tube or through the (failed) element rod.

This is my (poor quality) photo of a larger element, but of how it could look inside