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Thread: Water hammer only when water heater is on

  1. #1

    Default Water hammer only when water heater is on

    Hi everyone,

    We are having a water hammer problem in the bathroom. We have installed water hammer arrestors to the hot and cold connections for the sink in this bathroom but the problem still exists. We are thinking of going in to the wall but are not too happy with the idea since the wall is tiled.

    I was hoping someone here can offer some help. Here are the details:

    --Water hammer kncoking is coming from the bathroom

    --When we turn the cold inlet to the Water Heater OFF, water hammer disappears.

    --Turning the cold water inlet to WH back on makes the hammer come back

    --Our water pressure is 80 PSI

    --Bathroom has second farthest faucets to the water heater.

    Thanks.

  2. #2
    DIY Senior Member plumguy's Avatar
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    Default

    Have you tried shutting the water off to you're washer machine? Bathroom sinks are an unlikely place for hammer to occur. Focus on fixtures that are quick acting and I would start with the WM.

  3. #3
    Master Plumber master plumber mark's Avatar
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    Talking water hammer

    that seems really odd....is it a gas or electric heater?

    try what the other fellow said first, who knows..

    have you noticed if this does this only when the water heater is heating ??

    if it is gas, it might be a banging sound that does ocur when the unit
    is fairly limed up and in the heating cycle., if hot water is turned on wehn the unit is heating, it can make a loud rumbling, banging sound

  4. #4
    Moderator & Master Plumber hj's Avatar
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    Default knock

    Maybe the faucet needs to be repaired.

  5. #5
    Plumber jimbo's Avatar
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    Hammer occurs when running water is suddenly turned off. If you have noises when no water is running, it could be the WH as mentioned. 80 PSI is marginally high. 80 is actually considered to be the max allowed. High pressure contributes to hammer and other noise problems.

  6. #6
    Master Plumber master plumber mark's Avatar
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    Talking hi is probably right

    hj is probably right

    the best bet is a faucet washer is loose

    and chattering

  7. #7

    Default

    Thanks everyone,

    I had tried turning off both faucets of the washing machine and it did not eliminate the problem... WH probably contributing since the banging happens when we turn any faucet in the house off and the cold inlet to the WH is open at the same time. Our water heater is gas and I will check to see if it happens when it is heating.

    Would adding one of those expansion tanks help the relieve the pressure from the water heater?

    Will check the washers also and let you know.

  8. #8
    Forum Admin, Expert Plumber Terry's Avatar
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    I've seen heat trap pipe nipples at the tops of water tanks that have quit working right. I had to replace them on the job I was at. I wound up using my standard 3/4"x3" brass nipples with new 24" flexes.

  9. #9
    Plumber plumber1's Avatar
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    Default Noise

    Knock is probably right...or it may not be "water hammer".
    Could be a noisy water heater.........Dont open up the wall......

  10. #10
    Master Plumber master plumber mark's Avatar
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    Talking mistery problems

    ohh, I just love trying to diagnose these mistery
    problems while being "blindfolded "

    who will get it right??? the suspence just drives me crazy!!!

    Terry , you should start a contest and start
    giveing out points to the
    fellow who gets it right.

    Then the guy who racks up the most points over a year
    period wins a plunger with his name engraved in the handle.!!!

  11. #11
    DIY Senior Member plumguy's Avatar
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    Quote Originally Posted by brendis
    Thanks everyone,

    I had tried turning off both faucets of the washing machine and it did not eliminate the problem... WH probably contributing since the banging happens when we turn any faucet in the house off and the cold inlet to the WH is open at the same time. Our water heater is gas and I will check to see if it happens when it is heating.

    Would adding one of those expansion tanks help the relieve the pressure from the water heater?

    Will check the washers also and let you know.
    Also check for pipes that are not properly secured.

  12. #12
    Moderator & Master Plumber hj's Avatar
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    Default knock

    Since the problem, and your solution are somewhat illogical, in that the heater supply valve being open or closed should not contribute anything to a knock in the cold water piping, therefore an expansion tank will not absorb extra pressure, because there probably is none, but it will balance out any imbalance in the water flow. But are you sure you are not just hearing "pop corn popping" which is caused by nodule buildup in the heater and a "pop, pop, pop sound when the pressure decreases which would occur when any faucet is opened. If that is what you hear then the only cure is a new water heater.
    Last edited by hj; 08-08-2005 at 06:29 AM. Reason: text

  13. #13

    Default Same Problem, any more ideas?

    I am having the exact same problem with my plumbing. I have been trying to figure out how to stop the noise from my piping for quite some time now and the other day I decided to shut the cold water inlet to my waterheater off. The noise completely stopped. I could still hear the slight sound of water swooshing to about the same rythm as the noise before but there was no clang.

    The noise I have been having is not a violent bang but more of a "metal hitting metal" sort of noise. However, all of my pipes are securly fastened. It almost seems like something on the inside of the waterheater shifts and causes the clang, clang...clang

    I was going to install some more water hammer arresters but I'm worried that won't fix my problem. It happens from all faucets even if I don't shut them off very fast. I have asked the city about my pressure and they said it was about 75psi. I have not checked it out myself however.

  14. #14
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    Would a check valve, say in the water meter, cause that sort of noise if it was leaking under the pressure of the water heater expanding the water without an expansion tank?

    Since the noise stops when you stop flow into the water heater, it appears that it is something related either to it or the expansion it causes.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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