Plumbing Woes - water hammer cost ££ so far

The pressure setting of the reducer may need to be adjusted. There is an Allen screw in the end of the grey plastic cap that can be adjusted to raise/lower the water pressure to the cylinder.
Might only take a quarter turn up or down to make an improvement.

Does the grey cap just unscrew then as no hole in the end of it?

unfortunately to test it then means waiting for the hot water to heat up 🙄

Quarter turn on the ball valve above the control group would appear to isolate incoming mains, but you’ll still have (hot!!) water in the tank at pressure and at a level above the control group. So you’ll be wet and potentially scalded.

So you’ll need to (at least partially) drain the tank via the drain cock that’s fitted to the cold inlet pipe near the tank. Use a garden hose trailed to a lower level drain or out a door/window.

I’d strongly advise cooling the tank before attempting.

As for whether this will solve your problem, I have no idea. Has it developed recently or been like that since install?

Also, that flexi has no place on your hot water outlet. One day in the next ten years it will fail. In the meantime it’s also an unnecessary restriction on your HW flow.

IAMNAP

Aye it might.
The prv protects the cylinder by reducing the incoming main pressure down to 3bar, or just under. So make sure your turning it down.
Water hammer can be caused by shunting, where a shockwAve returns back through the system ehen a flow of water has abruptly stopped. Then it hits a restriction and bang
Sometimes a simple arrestor installed inline can stop it or an air tube tee'd off the high point acts ad a damper, the air cant escape as there is water below it and the air is compressionable.
Has the stop cock been switched off and not fully opened? This can cause a knocking. Doubt its the softener, that should help by their design.

Does the grey cap just unscrew then as no hole in the end of it?

If there’s no adjustment screw then you’ve probably got the preset (non-adjustable) version.

Again, IAMNAP, I could be miles out.

Under the end of a sticker that said 3 bar is just this pic below. Doesn’t look to be any way to adjust ?

Re water softener. We have been in the house 3.5yrs and fitted the water softener. The house is about 12yrs old so will have had very hard water for years

Edit. Having had a better look at the cylinder pics that is what you have.
So your plumber has already done what i suggested, and added in a random flexi, which is not good.
The reducing / relieving valve block thing might be popping on shut off. Any way to remove the relief outlet and shoot it into a bucket? Then tap test it

So your plumber has already done what i suggested, and added in a random flexi, which is not good.

he has added the arrestor to the hot out (don’t blame him for that) but the banging is definitely coming from the cold in.

would an arrestor need fitting before isolating valve on the cold in side or after it’s been through all those valves before it enters the cylinder?

really appreciate all the help !

This may sound stupid but you don't have a leaking tap somewhere do you?

We had this earlier in the year in our new home and a friend at a local plumbers trade counter said the noise could just be worn ceramic discs in the tap valve. They have just enough play to rattle and send vibrations through the system.

We changed the valve in the tap and the noise was gone.

the noise could just be worn ceramic discs in the tap valve

That’s a good one actually, I’ve heard this said many a time. The valve could be on the cold side - a sink tap or a toilet fill valve. It can be easy to rest if you have isolators near each tap and toilet. Isolate as much as you can and then test.

We had this earlier in the year in our new home and a friend at a local plumbers trade counter said the noise could just be worn ceramic discs in the tap valve. They have just enough play to rattle and send vibrations through the system.

it has been getting worse since we moved in to the house, however we had both bathrooms completely replaced. The noise stopped. Even the kitchen tap is less than 2yrs old

The only think that does drip is a downstairs toilet where water never quotes stops entering the cistern

The valve could be on the cold side – a sink tap or a toilet fill valve. It can be easy to rest if you have isolators near each tap and toilet. Isolate as much as you can and then test.

I better look at that toilet !

It's the shockwave travelling back through the system apparently, till it hits a restriction. Hot / cold is irrelevant, bit having said that
A length of 22 teed into the cold in, between the prv/prv ( its both, pressure reducing and releasing valve) wouldn't hurt.
Try the bucket under the red knob first, see if thays popping.

CaCo3 build up unlikely to be an issue as you have a softener. So hard water wont be a thing.

Then check the stop cock has been fully opened .

Disclaimer ianap

That will be calcium pn the fill valve seat, or fill valve seat grommets failure.
They are less than a tenner and an easy fix, if you can change a bottom bracket ypu can swap a fill valve

Do you have a cold water header tank. I'd be changing the fill valve rubber washers etc. Eventually found it.

Its an unvented, direct to mains cylinder. Hence the prv set up. So mains water enters the house ay say 4bar. The prv reduces this to 3bar, which is what unvented cylinders are rated at. You then, in theory, have 3bar pressure throughout the property which is perfect for showers and baths

IAAP with G3 which is the legally required qual required to work on unvented cylinders.
Firstly, don't adjust the pressure reducing valve, it's part of the safety mechanisms to stop the whole tank going pop in a spectacular and destructive manner!
The water hammer is most likely to a worn tap or valve seat, that WC float valve would be No.1 culprit in my eyes as a starter for 10.
Multivalve replacement is straightforward but again it should be done by a G3 qualified plumber.valves aren't cheap unfortunately. If could be accumulation of debris in the filter defecting that valve but I assume that was cleaned out when the plumber was there putting that random Flexi pipe in the hot water pipework!!
Also the pressure in the expansion vessel should be the same as the static incoming mains pressure, so that may need adjusting.
Try the WC float valve first though. Good luck

An update - I isolated the toilet and it made no difference.

The plumber rang me back - I was hoping he would be more helpful and agree to come out and try again, but no he said my wife and I should try and isolate the vibrating pipe. He then said that the pressure release valve would be £100 + VAT + fitting, which they appear to charge £80 for 30 mins.

Got the impression he really cant be arsed.

So do I change the PRV myself or do I need to get yet someone else new in?

You really shouldn't be working an unvented cylinder without a G3 qualification as @cannyj has said.

You really shouldn’t be working an unvented cylinder without a G3 qualification as @canyj has said.

Fair enough - this is going to get very expensive, and I dont like the fact they have done something already that doesnt make sense, even to me (ie flexi hose)

If could be accumulation of debris in the filter defecting that valve but I assume that was cleaned out when the plumber was there putting that random Flexi pipe in the hot water pipework!!

Did they buggery. They didnt do any fault finding just jumped to it being the hot water that was the issue after we said thats when it happened.

Unfortunately we have to keep using them as they installed our boiler, and they are the only people in the area who can service the boiler to maintain warranty

So do I change the PRV myself or do I need to get yet someone else new in?

Google unvented cylinder explosion and make your own mind up...

Oh and that flexi hose is a proper bodge. I can see what they are trying to do but that's not the right product or the right line size. As a temporary test yes.
Difficult for any plumber though. It's a bit like the creak on your bike.

Unfortunately we have to keep using them as they installed our boiler, and they are the only people in the area who can service the boiler to maintain warranty

Not heard of that requirement. Some of the very long warranty options maybe but most are xxyears warranty as long as serviced by qualified person.

Further update. Had another issue with a heating valve that was faulty and replaced , so I got the valve pack replaced at the same time (first pic at top of thread)

The banging has now gone when switching a hot water tap on, but weirdly now when you switch a hot water tap off there is a deep rumbling that goes on for about 10-20 minutes! It’s not mega loud but just loud enough to be very irritating!

Any ideas?

Try turning your pump speed and your boiler flow temperature down.