Dear UK.D-I-Y,

I have a strange clunk in my airing cupboard! I have an unvented hot
water system (tribune premier cylinder) with electric only heating as
we’re out in the wilds. Whenever a cold tap is turned off I can hear a
clunk coming from the airing cupboard, none of the pipes in there are
loose (they are all very solidly clipped), and I can isolate the noise
to the Pressure Reducing Valve (PRV). It seems that the clunk comes
specifically from this one valve. Is this something any of you
knowledgeable types have seen (heard!) before? Is this a standard way
for them to fail?

I have recently done a load of work to the system (moving a bathroom)
but this problem came on some weeks after that was finished. I have
tried fitting a shock-arrestor near the stopcock in the kitchen, but
sadly this made no difference, would it be worth moving this?

Does anyone have any advice on whether or not it’s worth changing the
valve? The fact that it’s an unvented system makes me a bit nervous
about diving in and messing with it. If this is a standard PRV failure
mode then I'll just change it.

Thanks in advance.