SylvanLMP
Hi what you failed to mention is that your father did not change the seats on these valves. I would also do the following. Try to isolate the actually hydraulic shock (water hammer) by having someone open and close these “taps” SLOWLY at 1st to see if it still happens THEN try it closing the taps a little faster.
Rather than running all over the place looking for a gauge try keeping this simple as looking for an unsupported pipe or a quick closing valve like a washing machine or dishwasher. I am sure if you really take your time you can find the exact pipe/ tap causing this condition.
Good Luck
