Water Hammer Despite Changing Pressure

Taylor1000 · Oct 23, 2017

Hi All

First of all I'll clarify that I am a homeowner and have very little plumbing knowledge, so some / all of my terminology will be very basic / wrong.

A few weeks ago my water pipes started 'clanging' when not in use, making the same sound of something shutting off as when I usually turn off one of the taps. It sounded like something filling up then locking to stop more water coming in (when I listened closely I could hear the water running then stopping as it clanged). My dad, who knows a fair bit about plumbing (but not in this instance) turned the stopcock up to nearly full, and that didn't work.

I then phoned my usual plumber who fitted my boiler, who said the issue is a water hammer and that I needed to turn the stopcock down, and that it could have been down to a change in water pressure in the area. I turned the stopcock down and it seemed to have solved it. But then it came back.

It now happens intermittently. It can be quiet for a bit, then happen a few times in 5 minutes, then regular intervals. It can also be louder at some times than others, and seems to be in different places depending on how much the stopcock is open. I've turned the stopcock down to about 1/3 of a full rotation at one point. Any lower and I'll lose flow in the taps. The only time it doesn't happen is when the water is off. I've drained the taps and started again and that didn't solve it either.

It's never done this before and I had a new boiler around 2 years ago. It even makes a noise when I come in from work and no one has used the water all day and the heating hasn't been on.

Any advice on how to solve this would be much appreciated.

Many thanks in advance.

Best · Oct 23, 2017

Turning your stopcock down won't reduce pressure and often makes things worse! All you are doing is reducing flow and putting the washer closer to its seat, which can make a noise and hammering.
Have your stopcock checked and replaced if it needs done. Also get any ball valve or fill valves repaired or replaced. Any loose mains pipes need clipped.
A pressure reducing valve fitted to mains after stopcock might help.
What type of boiler and water system do you have?

Taylor1000 · Oct 23, 2017

Best said:
Turning your stopcock down won't reduce pressure and often makes things worse! All you are doing is reducing flow and putting the washer closer to its seat, which can make a noise and hammering.
Have your stopcock checked and replaced if it needs done. Also get any ball valve or fill valves repaired or replaced. Any loose mains pipes need clipped.
A pressure reducing valve fitted to mains after stopcock might help.
What type of boiler and water system do you have?

Thank you for getting back to me.

I have a combi boiler. What do you mean by water system?

Is there anything I can do in the meantime that is the 'least worst option'? What do you mean about the washer being closer to it's seat?

Best · Oct 23, 2017

Combi boiler will usually mean all your taps are mains high pressure.
Turning down the stopcock just turns the rubber tap washer inside it to closer to where it seals (the "seat"). As I said, that can actually cause noise in itself.
On the subject of stopcocks - the part the washer is on is called the jumper and this whole part can make a noise if not properly pinned in. A new stopcock would then be needed.
I would begin with checking any ballvalves on toilets. Just simply a worn seal washer can cause water hammer. Old style toilet ballvalves on mains pressure are better replaced with Fluidmaster Pro B valves to prevent noise and possible water hammer.
I would also replace any stopcock and tap washers, plus any worn ceramic tap works (1/4 turn taps).
The water pressure needs tested and if very high could be regulated with a pressure reducing valve - PRV.
There are shock arrestors that can be used, but best to find out first if any other fixes work