If the water is being heated and it is not being pumped away from the heat exchanger there's a serious risk of an explosion - so an overheat cutout will operate after a short period.
It may be that the circulating pump on your installation is defective - I just guess.
Call in a specialist engineer who will soon sort it out.
I do not understand your expression - Holly House Power
If you mean the earth leakage breaker cuts off the electricity then that's another thing altogether and I have no explanation...
Good Luck...
February 2017
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