Our worcester greenstar he boiler sounds like a world war 2 lancaster bomber trying to take off ! This happens when it first switches on in the morning - whenever the hot tap is turned on - or it pumps water when the thermostat clicks it on. An engineer has suggested we should add an extra "tank" of some sort of repair Can anyone tell me what this is - is it a manufacturers recommended "fix" or what? Is it safe and is it normal to do this? also does anyone know where I can download a manual for this - I cant find one on the worcester site . have I just missed it? The boiler is 14 years old.