On 10/10/2009 18:06 Chris Hogg wrote:

Something else I've seen suggested is a flat baffle plate fixed
horizontally under the float on the ball valve in the cold water tank.
This helps stop the float from 'bouncing' and hence perpetuating the
knocking when a tap is turned off suddenly.

Thanks for the suggestion but, some time ago, I went up into the loft
and held the floats up to stop either of the valves from opening.
Management operated the cold water tap and the hammer was still there.

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F