I live in a semi-detached house approximately seven years old. I moved into the property in 2005.
The plumbing soil and vent pipe is capped at the top with a Durgo valve in lieu of the traditional penetration/ballon grating through the roof.
Every time hot water runs down the pipe, there is a hammering sound which starts off with a number of hammer sounds in quick succession. After a minute or two, the frequency of hammering slows and eventually stops altogether.
When the hot water stops, there is no hammering. When it is turned on again, the hammering starts again.
The strange thing is that when the cold water is turned on before the hot water , there is no hammering. But when the cold water is turned on after the hot water, there is some hammering.
This problem applies to hot water coming from any appliance (wash hand basin and shower in the first floor bathroom).
My guess was that there is some pressure anomaly in the pipe causing a reaction from the Durgo valve. I haven't replaced the valve since it seems to be working fine in terms of preventing foul air escaping.
Could the problem be something else? I would be grateful for your feedback
See our project on water hanmmer, the symptoms you describe are reminiscent of this problem. When you ask the tank for hot water by opening the tap, its there and is immediately replaced by cold water which obviously gets heated up. The cold inlet is controlled by a valve which more often than not is on a float, just as your toilet cistern is. The rest is explained in the project.
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