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!

Milo Dolezal

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 ?