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Thread: What Causes Repetitive Water Hammering?

  1. #1
    DIY Junior Member jimolson's Avatar
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    Default What Causes Repetitive Water Hammering?

    I have a condo with a 10 year old, 40 gallon electric water heater. I have city-supplied water. Obviously I'm due for a new water heater real soon. I live in a region with very hard tap water.

    Whenever a water valve is open in the condo (toilet, sink, or washing machine) there is a repetitive banging sound coming from the walls. I can also hear the sound in the water heater. The repetition rate is roughly 2-3 Hz. Some days the sound is so loud you'd think my neighbor is pounding on the walls with a hammer.

    Someone at the local water company suggested to me that the problem is due to an air bubble in the water heater arising from calcification of the heating element. That sounds plausible to me, but how does an air bubble in the water heater cause pipes to bang?

    What is the device in my house that is opening and shutting repeatedly and causing the banging sound?

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Make sure that the main shutoff valve is fully opened. Do you have a PRV? Does this happen with both hot and cold, or only one (and if so, which)? Have you checked the water pressure?
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIYer, not in the trades LLigetfa's Avatar
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    I have seen where loose fitting washer-style faucets would oscillate up and down like a jackhammer air motor does but that produces a sound like a woodpecker, much faster than 2 - 3 Hertz. If the sound is prevalent at the water heater, I wonder if it doesn't have an anti-perc device. My water heater has an anti-perc that makes loud clunks, but it only does it at the start and end of the water flow. Some water heaters have a mixing valve on the outlet that blends some cold to reduce the temp of the output. I'd look for some such thing as well.

  4. #4
    Jack of all trades DonL's Avatar
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    Hello Jim and the Group,

    Jim if it is in a Condo then it could be problems with anything within your building.

    I would recommend contacting the Maintenance Person for Your condo and have them check it out.

    If You pay for Condo Fees , Then Maintenance should fix it.

    Sounds like others could be having the same problems.

    Are any of your neighbors having the same problem ?

    Maybe its that neighbor lady wanting you to come over. lol.

    Have a Great Day.
    Theory only works perfect in a vacuum.

    Cyber Security Protection for Windows C:\ > WWW.WinForce.Net

  5. #5
    DIY Junior Member jimolson's Avatar
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    Default Repetitive Water Hammering: Problem Resolved

    I resolved the problem I posed to the forum last week. When I removed the 39 gallon low boy electric water heater it gave me better view of a tight nest of copper piping secluded in the closet wall behind it.

    The nest of pipes included a pressure regulator/reducer. The regulator appears to have been installed ten years ago when the water heater was replaced. This regulator is the source of the 3 Hz oscillation.

    When I adjust the screw on the front of the regulator, the frequency and intensity of the oscillation changes. I think that counter-clockwise adjustment of the pressure setting screw is the preferred direction, likely reducing the output pressure.

    I verified that the street valve is completely open, as is the mains valve in the condo.

    The water flow rate that triggers oscillation is quite low. Flushing a toilet is sufficient.

    Is the regulator oscillating because of lime build up in it? A pebble wedged into it?

    The suggestion that the problem was an air bubble in the water heater appears to be wrong. A new water heater did not affect the problem.

    By the way, there's an amazing amount of pea gravel-like stuff that washes out of a ten year old water heater when you up-end it in the driveway.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    The PRV may be shot at 10-years. Also, when a PRV is installed, you also need an expansion tank. You can buy an inexpensive water pressure gauge for around $10. Get one with a peak reading hand (tattle-tale) and install it and leave it for say 24-hours. Note what the peak reading is, and your current value. It is generally recommended to install a prv when the pressure exceeds 80psi.

    If you flush the water heater periodically, you'll remove a lot of that mineral buildup and it will work better, longer.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7
    General Engineering Contractor ballvalve's Avatar
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    Moral of story - Do not hide PRV valves. Install a full bore valve in the weater heater clean out and use a coat hanger or vacuum adapter every few years to suck the calcium out. Then change the anode every 5 or ten years.

    And dont toss the old rig - its still fine.

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