Hot water pipes clanging when hot water turned on/off

UnsureAboutthis

What's a PVR? The stopcock is a small cutout under the sinks and it was very stiff and I had to cut through the  4mm backing board to get better access.

Speaking to my regular plumber about 30 mins who retired a few years ago, he said take off the side panel of the bath and see if loose pipe clip etc as only hot taps doing it. I will look at that possibly tomorrow as relatively easy to remove and if it does not work, as I said the stopcock is in a tight place and I don't want o have the sturdy backboard damaged further but may need to
Thanks to you and everyone.

UnsureAboutthis

Jut looked up PRV - its cumbersome - Can't i just turn the stopcock down a bit?

UnsureAboutthis

Just did a test. I first turned on the cold tap at 1/3 speed approx - no hammer nosie on bath tap. Then i noted if I flushed the bathroom w/c and seconds after turned on the hot bath tap, no water hammer noise.

ThisIsWeird

UnsureAboutthis said:

Just did a test. I first turned on the cold tap at 1/3 speed approx - no hammer nosie on bath tap. Then i noted if I flushed the bathroom w/c and seconds after turned on the hot bath tap, no water hammer noise.

That's promising - by taking some of the pressure and flow away by opening another tap, the issue is improved.
In response to your other Q, about whether just turning down the stopcock will do, the answer is 'yes' in that it'll almost certainly reduce the symptoms, but it'll also reduce the available flow to your taps. So if you, for example, now run two taps at the same time, or a shower and washing machine, you will most likely notice the loss.
And, when the taps are closed, the pressure will be as high as it was before, but will just drop more dramatically when a tap is opened.
The whole point about a PRV - not bulky at all - is that you can reduce the pressure, but maintain the flow.
If course, it's only guesswork at the moment that excessive P is the problem. You need a pressure gauge to measure this, but a good idea can be had by how forceful the water comes out your kitchen cold. How gushy is it?

UnsureAboutthis

Many thanks again. In the kitchen, we have very good pressure and it his the steel sink hard but not splash out as its a very big, wide, deep domestic kitchen sink but the pressure is really good, very "gushy" as you put it even the hot water is,

I now understand what you are saying re PRV - but the kitchen is like new and all the pipes are hidden, so will need holes

Why do you think it was running fine then a few months ago, most likely over a year this started to happen and we've not had anything done to pipes etc.

It is denfinetly hammering less if i turn on the cold tap first even part turn or the cistern is filling up.

ThisIsWeird

No idea why it's happening more now. Has anything changed? Inside or outside work on the mains? Stopcocks adjusted? 
Where is your internal mains stopcock? And where does the pipe run afterwards? 
Of course, I am only guessing that the cause is excess pressure, and really it's worth measuring. It could possibly be a pipe that has come loose, and is moving excessively.
But, a distinctive and louder-than-usual shhhhhh-roar noise when taps are running does suggest high pressure and flow too.

gm0

Another possible cause of hammer.  Is a failed - life expired - shower mixer valve setup.

Not all types of mixer.  But sometimes simple ones with a failed or never fitted non-return setup can "connect" hot water to cold to a greater degree and it can cause groaning/hammer when less than 100% clipped pipes vibrate

We had tried lowering pressure, prv, surge arresters, adding extra expansion vessel on pressurised hot water.  Nothing worked. Though the resonances were shifted.

Then we replaced that particular shower and all issues disappeared entirely.

UnsureAboutthis

Ok, thanks all, lots to consider, do etc
The little bit of good news is via your help, I've ascertained that the hammer on the hot bath tap which is really bad is down to zero if we turn on the cold tap on the basin

Btw, we are waiting for a new bathroom, and shower room and the current mixer o the bath taps in non-operational nor do we use the cold tap as both are very hard to close. Thanks again

UnsureAboutthis

 I've just noted the sink hot tap nearest to boile does not make any noise at all ue hammer type

ThisIsWeird

I'd personally wait until all your new bath and shower rooms are done, and take it from there
You never know...