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Thread: Hellow and knocking noise in water pipes when running dishwasher

  1. #1
    DIY Junior Member Skyla's Avatar
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    Question Hellow and knocking noise in water pipes when running dishwasher

    Hi, I'm a home owner - house is 14 yo. DH and I are not handy but I'm thrilled to find this forum where I can ask a question about a problem I'm having - thank you Terry Love. I have researched the internet and can't find anything so I'm hoping maybe someone here knows what the problem is ... and hopefully the solution.

    Every time we run the dishwasher we get horrible loud knocking sounds in the water line as the dishwasher is pulling in water. When we run the kitchen faucet the noises stop.

    I've had two highly recommended plumbers to the house about this problem. The first one said it was my faucet in the sink next to the dishwasher which was loose and replaced the parts and for awhile it was slightly better. The second one claimed it was air trapped in the pipes, drained all the water out and fiddled around - that didn't help. He also took apart the water on/off turn offs to check if there was any grit or something interfering with the seals - everything looked completely normal. He then suggested the it was the dishwasher but said he had no knowledge how dishwashers worked or what the problem could be.

    I believe the dishwasher is about 7-8 years old and appears to be working properly - dishes come out clean within an appropriate time frame. The machine interior is clean - no build up of debris or clogged lines and drains completely.

    My hot water heater is also about 7-8 years old. We have plenty of hot water for showers so I'm not sure if that is the problem? No knocking when taking showers or flushing toilets.

    I need to fix this problem - we can't keep running to the kitchen to run the tap when we run the dishwasher. I don't want to pay another plumber who can't fix or at least diagnose problem.

    I don't want to pay for a dishwasher repair person to come unless it is the dishwasher. And if it is the dishwasher - is it a part that can be repaired or would I need to replace it? Every time I call the appliance repair person they can't fix it and I have to buy a new one - these appliances are designed now to break down and not be repairable. I'd hate to buy a new dishwasher only to find I still have the same problem.

    Thanks in advance for any suggestions.

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    I would add a hammer arrestor to the dishwasher supply.

    Places that the code book lists for hammer arrestors if the water supply system is closed.

    Dishwasher
    Icemaker
    Washer

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    DIY Junior Member Skyla's Avatar
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    Quote Originally Posted by Terry View Post
    I would add a hammer arrestor to the dishwasher supply.

    Places that the code book lists for hammer arrestors if the water supply system is closed.

    Dishwasher
    Icemaker
    Washer
    Thank you for your quick replay - is this something a plumber does or a dishwasher appliance repair person?

  4. #4
    Forum Admin, Expert Plumber Terry's Avatar
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    This can be installed inline with the water supply.

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    DIY Junior Member Skyla's Avatar
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    Perfect, thanks

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The things Terry listed all have one thing in common...they all have quick acting water shutoff valves (typically a solenoid valve). Anything moving has inertia, and stopping it quickly needs a release of that kinetic energy. A hammer arrester does that by having a piston with trapped air on the other side...the water keeps moving, but instead of bouncing the pipe off the wall into something, it pushes that piston against the trapped air, absorbing the energy, keeping things from bouncing around.

    You've probably seen the hoses on your washing machine jumping when the water turns off...you need some there to help protect those hoses from rupturing as a result of that spike. You can buy those at a big box store that just screw onto the shutoff valves, then the hoses screw back onto the new arresters. No tools required, expect maybe a pair of pliers if they're on there tight.
    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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    DIY Junior Member Skyla's Avatar
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    Jim, Thanks for that information - very helpful.

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    DIY Junior Member MIKE007's Avatar
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    Is there a specific position for a hammer arrester? Can be installed in a horizontal position?

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    Forum Admin, Expert Plumber Terry's Avatar
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    Is there a specific position for a hammer arrester? Can be installed in a horizontal position?
    I tend to install them vertical, but since it's a piston with air behind it, it doesn't matter. They are non-directional. They go on the end of the run, or within six feet of the end.

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