Just trouble shooting getting a few knocks (water hammer) in our house. 1960s build with copper piping. Renovations done a few years back so some of the plumbing has been updated to modern buteline as follows:

Metered tap at boundary through 15mm copper pipe to house (about 25m), converts to buteline and services bathroom shower/vanity, then goes back to old 15mm copper pipe to service the kitchen (sink & dishwasher)  and lastly the laundry (washing machine / tub) and outdoor garden tap.

Hotwater is via a gas califont near the bathroom.

We used to get bad water hammer that all but disappeared when the new plumbing section was installed, however I have noticed lately that we do get fairly minor knocks that seem to be at the laundry / copper end of the system that are mostly apparent when the dishwasher is active.

I've made a pressure tester and the system reads around 80psi (550kpa) at the far end of the house (garden tap). My understanding is that Auckland mains should be max 500kpa, and most piping is rated to max 550-650kpa.

As a side note in the 14 years we've had the house I've had to repair 3 instances where the copper piping has split or developed pin hole leaks, so I'm suspecting that the pressure is a little too high for old pipes anyway...

So answer seems to be a pressure reducing valve up by the meter, but before I engage a plumber do we think that bringing the pressure back to under 500kpa will most likely eliminate the knocking? I also have a surplus and hardly used water hammer arrester but I figure if over pressure is the issue its best to reduce rather than use the arrester to mask the issue.

Opinions welcome.

Thanks

Ben.