We'd like to remind Forumites to please avoid political debate on the Forum. This is to keep it a safe and useful space for MoneySaving discussions. Threads that are - or become - political in nature may be removed in line with the Forum’s rules. Thank you for your understanding.
We're aware that dates on the Forum are not currently showing correctly. Please bear with us while we get this fixed, and see Site feedback for updates.

Knocking pipework?

Hi there,

We're unsure if this is related to a pressure change within the area (we recently had Southern Water digging up the road and having to turn off the water for a short time to do some work) or something completely unrelated.

Within the last couple of months we've noticed that the pipework around the house will "clang" when turning off the mains water either via any of the taps or when using the washing machine -it's a sortof "knock, knock, knock" sound. The noise will continue for some time and then eventually settle down but it takes a long time to do so.

I've think I've narrowed it down to a particular pipe run which is situated next to some hardboard which someone decided to put in as a kindof false ceiling I presume as the boiler was moved from one of the bedroom cupboards into the roof at some point. When the taps/washing machine is run, my guess is that the pipe is knocking on this as there is a little bit of play in the pipe.

There are several joints to this pipe which runs:
  • From the kitchen
  • Into the cupboard under the stairs
  • Up into the landing area
  • Across the landing into a bedroom into a cupboard
  • Up from here into the roof to connect via the cold water feed tank
I could of course just cut into the hardboard where the pipe is and it will stop at least some of the knocking but as far as I can tell it's also knocking further down the pipe in the cupboard under the stairs.

I asked the heating engineer who installed our boiler about a year ago to take a look when he did the boiler's annual service, but annoyingly we couldn't replicate the issue. We then managed to capture a video of the knocking and he recommended that we clip the pipes in place and also install a mini expansion vessel - he offered to do this for £160+VAT parts and labour but this doesn't seem to be a definite fix - just a "try and see".

Before I call in some plumbers to take a look and quote on any work I thought I'd make a post to see if anyone else has any ideas what may have caused this to happen and what possible fixes there are? As I say it's only been doing it in the last couple of months and there's been no change to our system since the boiler was installed.

Thanks in advance!

Comments

  • Ayr_Rage
    Ayr_Rage Posts: 1,969 Forumite
    1,000 Posts Second Anniversary Photogenic Name Dropper
    Most likely air in a pipe, run all your taps and outlets for a while.

    Turn down the main stop valve so that there isn't excessive pressure coming into you home.
  • twopenny
    twopenny Posts: 6,882 Forumite
    Part of the Furniture 1,000 Posts Name Dropper Photogenic
    I tried this when one of the pipes started knocking on flushing the loo.
    Eventually I turned the stop tap down just a tad and that did the trick. 
    Think I increased the flow at the stop tap to run the garden tap better at some point and I'd increased the amount of water in the toilet cistern - it took a while to object.


    I can rise and shine - just not at the same time!

    viral kindness .....kindness is contageous pass it on

    The only normal people you know are the ones you don’t know very well


  • Shoxt3r
    Shoxt3r Posts: 171 Forumite
    Eighth Anniversary 100 Posts Name Dropper
    Great thank you - I did wonder if it was air in the pipes. Will try running the taps and reducing the pressure via the stopcock and see if that helps.

    If it doesn't I guess we need to get a plumber in to get a second opinion?
  • grumbler
    grumbler Posts: 58,629 Forumite
    Part of the Furniture 10,000 Posts Name Dropper Photogenic
    edited 27 July 2023 pm31 5:53PM
    Ayr_Rage said:

    Turn down the main stop valve so that there isn't excessive pressure coming into you home.
    It controls the flow, not the static pressure. it will remain hight when there is no flow. I can imagine some sound produced when flow starts and pressure drops.  If so, it makes more sense to open the valve fully to reduce the pressure change.

  • Shoxt3r
    Shoxt3r Posts: 171 Forumite
    Eighth Anniversary 100 Posts Name Dropper
    grumbler said:
    Ayr_Rage said:

    Turn down the main stop valve so that there isn't excessive pressure coming into you home.
    It controls the flow, not the static pressure. it will remain hight when there is no flow. I can imagine some sound produced when flow starts and pressure drops.  If so, it makes more sense to open the valve fully to reduce the pressure change.

    Opening the stopcock wouldn't increase the pressure by allowing more of it in then? Yes, the knocking/hammering only happens after the water has been shut off - either by the tap being turned off or the washing machine stopping its draw of water. It also doesn't always happen straightaway as there could be a few minutes after the water has stopped flowing before we hear a knock, sometimes several times over.
  • grumbler
    grumbler Posts: 58,629 Forumite
    Part of the Furniture 10,000 Posts Name Dropper Photogenic
    Shoxt3r said:
    grumbler said:
    Ayr_Rage said:

    Turn down the main stop valve so that there isn't excessive pressure coming into you home.
    It controls the flow, not the static pressure. it will remain hight when there is no flow. I can imagine some sound produced when flow starts and pressure drops.  If so, it makes more sense to open the valve fully to reduce the pressure change.

    Opening the stopcock wouldn't increase the pressure by allowing more of it in then?D
    It controls the flow, not the pressure. Unless it's fully closed, the pressure in the house remains the same, high, and drops when flow starts. If the stop valve is almost closed and you open all taps on the ground floor, the water might never reach the first floor because the pressure gets too low.
    Yes, the knocking/hammering only happens after the water has been shut off - either by the tap being turned off or the washing machine stopping its draw of water. 
    Correct. Water hammer happens when flow stops sharply.  Pressure doesn't have to be high.
    It also doesn't always happen straightaway as there could be a few minutes after the water has stopped flowing before we hear a knock, sometimes several times over.
    This I can't explain. Hot water pipes make some sounds, not loud, when expanding and contracting



  • stuart45
    stuart45 Posts: 4,597 Forumite
    Sixth Anniversary 1,000 Posts Name Dropper
    I used to get it in the roof space after the water had been cut off for work in the road. It used to start when the valve was starting to close, and lasted a few minutes. Sounded like a low flying plane.
    Changed to an unvented system now, so nice and quiet up there.



  • A bit of an update on this - we've recently had an arrester fitted to the pipework next to the washing machine which has improved things on that front but we are still getting a hammering noise from the remaining pipework. The engineer didn't think that we needed to have our pipework clipped and the arrester should solve the problem, or at least help dramatically. He said that if we did notice any further hammering that we should reduce the pressure in the system by loosening the stopcock and see if that helps.

    Over the course of the last 2-3 weeks I have been gradually loosening the stopcock - I started by fully tightening it and then loosed by 4 turns. I've then loosened it by a further turn week by week. I imagine the number of turns is a bit subjective as every stopcock and setup will be different? If anything the adjustment to the stopcock seems to have made it louder and more frequent?

    The hammering when our washing machine was running (feeding water/draining) appears to have stopped altogether, so we now get knocking when the taps are run and strangely when the water heat turns on as scheduled during the night (around 5am).

    As I say, this appears to have all come about due to a change in the water pressure locally. I contacted Southern Water but they didn't want anything to do with it and suggested that we get a plumber in to take a look at our expense.
    We did get a new boiler fitted earlier in the year but this seems unrelated as the water hammering only appeared to happen after seeing Southern Water repairing an apparent leak further down the street.

    What are our next steps? Do I just keep turning the stopcock down, or even start from the beginning and loosen it all the way and then tighten it to see if that helps, or forget this idea altogether and get someone to look at the pipework again? The engineer we had seemed a bit vague about what the cause could be so I'm unsure whether to get him back, otherwise it's like throwing money away just to find the cause if we can get someone else in to hopefully fix it once and for all.

    Thanks in advance!
  • Water hammer is more often than not caused by a faulty tap or fill valve in your cistern(s)

    For example a friend of would cause water hammer through her pipes (and annoying her neighbours in the upstairs flat!) because of a faulty cold water tap in her kitchen. This happened when she flushed her toilet , changing the cartridge in the tap solved the issue 

    Do you have isolation valves on your taps and cisterns (toilet, f and e tank, cold water tank?) If you do recreate the water hammer , then close the valves one by one and see if you can recreate the issue , if you can't recreate the issue when a particular valve is shut then bingo! (Especially at 5am!)
  • ThisIsWeird
    ThisIsWeird Posts: 7,694 Forumite
    1,000 Posts Second Anniversary Name Dropper
    edited 12 October 2023 pm31 11:52PM
    Back to basics, Shoxt, and apologies if some Q's have been asked before.
    1) What type of boiler and water system do you have? Combi? Vented? Unvent?
    2) Any noticeable change to the mains recently, say following SW's work? Has the flow and pressure coming out your cold kitchen tap noticeably increased?
    3) When - exactly - does the noise occur? What - exactly - does it sound like?
    4) Anything else? Eg, are some taps and toilets more noisy than before when run? A louder water hiss? Anything at all?
Meet your Ambassadors

🚀 Getting Started

Hi new member!

Our Getting Started Guide will help you get the most out of the Forum

Categories

  • All Categories
  • 348.4K Banking & Borrowing
  • 252.2K Reduce Debt & Boost Income
  • 452.5K Spending & Discounts
  • 241K Work, Benefits & Business
  • 617.4K Mortgages, Homes & Bills
  • 175.7K Life & Family
  • 254.2K Travel & Transport
  • 1.5M Hobbies & Leisure
  • 16K Discuss & Feedback
  • 15.1K Coronavirus Support Boards

Is this how you want to be seen?

We see you are using a default avatar. It takes only a few seconds to pick a picture.