I've recently moved into a mid-70s two-storey detached house. The house has a new Worcester Greenstar C/H system, installed just before we moved in.
The problem is that first thing in the morning when the hot tap is opened there is a LOUD noise like a hammer-drill from upstairs, lasting for up to a minute. This only happens if the tap hasn't been opened for several hours. If the tap is closed while this is going on, the noise takes a couple of seconds to fade away. I can feel a couple of the pipes in the airing cupboard vibrating strongly, particularly a flexible hose that goes to what seems to be some sort of pressure vessel above the H/W cylinder.
The installer has been back and said something about air in the system causing this problem. He reckoned that he had fixed it by doing something in the loft (ball valve?) but the noise returned after a couple of days. Before I call him back again can someone please give me a clue as to what might be happening? Just to guard against bullsh^W flannel, as it were.