Overflow when hot water on??

[soma1980]

Hi, whenever our hot water is turned on the overflow pipe protruding from the side of our house starts to leak (sometimes just a drip other times a constant flow) - any ideas???? It's driving me nuts and where the pipe is positioned means the water drops onto our downstairs window which is causing its own problems.....

 

[Aquaheat]

Sounds as if the water level in the storage tank is too high and is not allowing enough room for expansion