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Thread: Mystery pipe thumping (not water hammer)

  1. #1
    DIY Junior Member jjtrindc's Avatar
    Join Date
    Jun 2006
    District of Columbia

    Default Mystery pipe thumping (not water hammer)

    Posting again with updates and a call for advice on continuing ďtickingĒ noise Iím getting from my pipes. Iíve been able to shoot some video to capture the issue in hopes that I can give this group a better sense of what is happening.

    As background, I am on standard city water. My set-up along the main line includes a whole-house water filter, water meter and PRV valve (see picture) with a hot water tank about 5-6 feet away. The PRV valve was replaced about 9 years ago and the whole house water filter was installed approximately 6 or so years ago. The hot water tank was also replaced about 6 or so years ago.

    Here is a photo of the setup:
    Name:  Plumbing_mainlinesetup.jpg
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    During this time we had no issues. Then about 10 months ago we started noticing that the pipes had started making various noises that including ticking, thumping, and squeaking. I think it may have started even earlier but was something that didnít really catch our attention. Now the noise fluctuates from barely noticeable to waking us up in the middle of the night.

    Here is a video that attempts to capture the noise. It captures some of the squeaking but the ďthumpingĒ didnít come through in the audio (but its there). Note when I close the water supply toward the end that the squeaking noise really jumps.

    There is no rhyme or reason that we can figure out for why it happens, though it tends to happen more in the morning and evening. Working from home today the noise stopped being noticeable at around 10am, except for a brief period at about 2pm.

    Here is what we have done:
    -Eight months ago we replaced the water meter at the suggestion of our plumber. That didnít work.

    -We then replaced the PRV valve. The noise picked up again after about 48 hours.

    -We tested toilet leakages to see if anything was pulling water. They were all fine.

    -We replaced the line and filter into the upstairs freezer. No change.

    I called another plumber out who immediately felt that the PRV was faulty. He put a water pressure test gauge on the outside nozzle. The pressure was in spec, about 60 PSI, but then it started to rise about 6-8 psi and then fall again. This happened a couple of times. He suggested I monitor the pressure myself and then call the original company out to replace the PRV under warranty.

    I installed my own test gauge with a tattle-tale needle. Things were fine at about 58 PSI, but then I came out later and saw that it had jumped to about 66 or 68 PSI depending on how you interpret the reading. I then heard the noise and went to look at the gauge and found it jumping up and down.

    Iíve attached a video of this happening.

    So Iím prepared to call out my original plumber to talk about replacing the PRV based on the above, but thought I would check in here for advice first.

    Couple of other things:
    -I do not have a water expansion tank, and am completely confused about the need for one. Iíve read online that I absolutely need one, but both of my plumbers have told me that I do not and they are both highly rated on Angieís list. There is no leaking from my hot water tank at all.

    -I did see a suggestion that if I turn off the hot water heater I could monitor the test gauge and see if that changes. If it doesnít that probably confirms need for expansion tank. Does that make sense?

    -Iíve also seen another thread where the issue is the whole house water filter having a check valve:

    I could try to switch out my water filter as well with one that does not have a check valve.

    Having said that, Iíve had my current setup for a number of years without issue, so Iím reluctant to add an expansion tank or replace the filterÖthough I guess at some point, I have to try something!!

  2. #2
    DIYer, not in the trades LLigetfa's Avatar
    Join Date
    Feb 2011
    NW Ontario, Canada


    My guess is the noise is coming from the heat traps on the HWT. Turning off the water to the tank should confirm it. If it really bothers you, remove the traps.

    You should install an expansion tank.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    A PRV has an internal check valve. It MIGHT have a bypass valve, but it won't open until the house's water pressure exceeds the street pressure, so, if it opens at all, your pressure rose, which was why you wanted the PRV in the first place! The only way to prevent that pressure rise (at least accepted by the industry and codes) is to install an expansion tank. Otherwise, depending on how much hot water you use, and whether water then stops being used so there's no pressure relief, the pressure has no place to go but up. Depending on the type of piping you have, it could be expanding the pipe (as in pex), or the supply hoses to the toilet(s) and the sinks and the WM, assuming you don't use a shutoff to them (you should!). The weakest valve in the house tends to be the toilet fill valve, so water may be leaking into the toilet, sometimes it makes noises, sometimes it doesn't. WHen the PRV starts to go, that pressure buildup might cause its internal seals to leak, when they normally wouldn't. Regardless, closed system, expansion tank - they go together like peanut butter and jelly...you shouldn't have one without the other!
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    Forum Admin, Expert Plumber Terry's Avatar
    Join Date
    Aug 2004
    Bothell, Washington
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    One of my customers was affected by the next door neighbors home. You may want to knock on their door and see if they're having issues.
    You may all be on the same line.
    With the above mentioned situation, closing a valve quickly next door was hammering their home next door.

    I wound up installing a large hammer arrestor "before" the PRV.

    Heating water will affect pressure too.

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