I have a gravity hot water boiler with a hot water tank upstairs (indirect cylinder), The boiler heats the water OK but in the morning the hot water is only just warm. The only thing that I have noticed is that the feed to the header tank is always dribbling and never shuts off. I have looked for a leak in the hot water pipes but am unable to find one. Very strange!

:confused:

When you say "warm"... do you mean entire tank of hot water is warm ? Or only water coming out of your faucet for the first few minutes ?