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Thread: Plumbing knocks when water runs

  1. #1
    DIY Junior Member Treebeard's Avatar
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    Default Plumbing knocks when water runs

    Howdy. Have a three story (counting finished basement) house built in 2001. 3 1/2 baths. PVC pipe. Only real change to plumbing was summer of 2010 when hot water heater was replaced. No real problem for 11 years but recently plumbing has started knocking when water runs. Specifically, when certain toilets (mainly one in basement), sinks, etc. are run, the pipe attached to the main supply line moves back and forth and it sounds like the water is pulsing through the line rather than flowing continuously. I'd guess at a frequency of about once a second. This causes a noise as the moving, surging, pipe shakes the attached plumbing, including the tank (expansion tank??) on the supply line to the water heater (located right next to the main supply line). After doing a search on this problem on the Internet, I have twice turned off the main supply, opened every faucet and flushed every toilet, drained out all water, then closed all the faucets and slowly turned the water back on. Doing this twice has resulted in a lot of improvement, but the knocking (now diminished) continues when some of the toilets are flushed and always when the basement toilet is flushed. Please note this happens after the toilet is flushed and the tank is filling, not after the valve closes.

    Any suggestions of what to try next or possible causes?

    Thanks,

    Steve

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    Knocking during refill can indicate a bad shutoff at the wall, and the valve being partially turned down. Sometimes, even with a bad shutoff, if it's opened all the way you can reduce the flutter in the loose washer.
    You might also look at the fill valve on that toilet as a source of vibration.

  3. #3
    DIY Junior Member Treebeard's Avatar
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    Hi Terry, When you mention a shutoff at the wall, are you talking about the shutoff valve for the toilet? Please note that more than one toilet causes the noise. I believe the valve is opened all the way but will check it tonight. Would a loose/defective washer cause a rhythmic vibration with a very regular pulsing?

    The toilet valve is a fairly new Fluidmaster. How reliable are they?

    One thought I have searching through other posts on this forum, is could my water meter be suspect? Is there a way to test/tell?

    Thanks for any help

    Steve

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    Big Canadian bigjohn2012's Avatar
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    It could be either the shut off at the wall, or main coming up. I would replace the one by the wall first as its easier process of elimination

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