Circuit Breaker Keeps Tripping?

I have the Geyser breaker tripping on the DB board in the granny cottage.

I was told it could be the Geyser (water heater) element and thermostat so I changed them, but it still tripped. I then brought the element to my place of work where it was tested and it seemed to be faulty, I replaced with a new element and it tripped again.

The switch only trips after about 5-10 minutes when the water is luke warm.