hi put in a new direct tank, after three months the over flow started leaking changed ball value, still leaked you can turn off water at stop cock and it still leeks down over flow
header tank is cold and level of water in header tank when cold is 75mm below over flow, as soon as you turn on heater within two hours water has rision so that it comes out of overflow , have put new thermostat as well one you have to reset if you get power cut, so would it be a faulty thermostat