Judder / water hammer with an unvented HW cylinder

[Mathew Newton]

We've recently moved into a new(ish) house with a Range Tribune unvented HW cylinder and are suffering (being annoyed by) juddering / water hammer and would be grateful for some advice as to how to eliminate it if possible.

Some observations which may or may not be relevant:

1. The noise appears to be coming from the pressure reducing valve (and not loose pipework etc) fitted adjacent to the cylinder.
2. The expansion vessel pressure is 3 bar (measured with the incoming mains off and a some taps open) as per the manufacturers installation instructions.
3. The incoming water pressure is 2 bar (measured before and after the PRV).
4. The PRV setting is unknown.
5. The noise is a single thud from the PRV when a tap is opened and, more evidently, when it is closed. The cold water taps appear to cause a louder noise than the hot. Even the kitchen, connected straight off the incoming mains (i.e. upstream of the PRV) causes a thud.
6. The shower, particularly when first used in the morning, causes repeated thuds for half and second or so if turned on quickly.

Does any of the above point to anything in particular? Are there other details I've missed out that could be pertinent?

Grateful for any pointers,

Mathew

[mathewjamesnewton]

Yeah that's what I was thinking. And, if in 'normal' circumstances the role of the PRV is to limit the working pressure to 3 bar then to me it is understandable that the EV should also have a pre-charge pressure of 3 bar such that it is in a neutral state prior to heating. If I can only reach 2 bar then mine isn't in this state and, as say, going to have less of an effect.

Will drop the pressure a bit and see how things go.

Mathew