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Thread: Banging pipes

  1. #1
    Join Date
    Oct 2008
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    Default Banging pipes

    I have a forced hot water system (oil heat). When the heat comes up there is a banging and clunking for about 15 minutes. Last year I had the circulator replaced on the advice of my heating company (and of course it wasn't covered by warranty.) It seemed to get better, but it's back this year! I thought I'd ask here before I call them again and possibly replace something that isn't causing the problem.

  2. #2
    Join Date
    Jun 2007
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    Coventry, RI
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    Default Re: Banging pipes

    You could have air trapped in the system that is causing it. You could try bleeding the baseboard or radiators. There should be a bleeder screw on the each baseboard. Turn on the heat and let it warm up a bit and start with the one farthest from the boiler and work your way back. Be careful as hot air and water will come out of the bleeders when you open them. If that isn't the problem it is possible that you have to much pressure in your system. Do you have an expansion tank near the boiler? If not you may need to have one installed. If you do have one its possible that the air bladder inside has failed and is not absorbing the expanded water when it is heated. This could also be the source of the air in the system. Other things to look for are water pipes that are coming into contact with framing members as they will make noise when they expand and contract although this would most likely be more of a squeaking noise but could be banging. Hope this helps you out.

  3. #3
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    Aug 2007
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    Default Re: Banging pipes

    Unfortunately we don't know exactly what type of hot water system you have.

    See if you can identify yours from these explanations and then see the troubleshooting section for it near the bottom of that particular system's page.

    http://www.heatinghelp.com/heating_qa.cfm

  4. #4
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    Oct 2008
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    Default Re: Banging pipes

    Thanks both of you for your responses. My system is a diverter-tee system. Those explanations were great. Since it has a circulator I ruled out the gravity system. So does this give any clearer idea of the problem?

  5. #5
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    Default Re: Banging pipes

    Not sure exactly what the source of the noise is, but I've personally never encountered a circulating hot water system that made banging or clunking noises because of air in the lines. Not saying it doesn't or couldn't happen, but have not seen that myself. IME, air in the lines causes circulation problems and consequently convectors that don't heat up at all or poorly. Bleeding the system of the air usually resolves that sort of problem.

    So....I'm more inclined to think the problem is one of the others mentioned before; a water-logged expansion tank or pipes causing bangs and clunks as they rub against the floor boards. (Assuming this is actually a hot-water system and not a steam heat system)

    When the water is heated, it expands. That expanding water needs somewhere to go and if the expansion tank is water-logged, it doesn't have it. This can and will cause water-hammer. Hypothetically and hopefully, there should be a pressure relief valve somewhere on the system that would then pop-off/open temporarily and spill some water onto the floor.... if the tank was water-logged and pressures then became too high. That valve may be malfunctioning/failing to open when it should. This would not be a good situation and so if you discover anything indicating that this may be the case... I would recommend replacing that valve.

    Depending....your system could have a single compartment galvanized tank or a newer bladder-type tank. It would not be that unusual to find a galvy tank water-logged, particularly if it was never equipped with a device to maintain the water to air ratio...or if that device is now malfunctioning. Renewing the air-head in such a tank is not that difficult to do....as a rule. Close the valve on the water inlet pipe to the tank (usually right there close at hand by the tank), drain the tank completely via its drain valve, close the drain valve and reopen the supply valve. (Completely draining a tank can take quite a while if there is nowhere to/provision for allowing air in at the same time. If this is the case, you may need to allow the water to drain (thru a short length of garden hose) until it stops or nearly so and then blow some air into the tank (mouth over hose end) . Drainage can then commence again.)

    (There are potential complications that could arise and/or be a contributing cause of the reason a tank is currently water-logged....related to a failed or failing automatic pressure control valve on the supply pipe to the boiler itself...but I/we won't go there unless needs be.)

    If a newer type bladder tank, it really shouldn't be water-logged unless the bladder is ruptured/torn. It may be. Replacement would then be in order...or the best option anyway. To check if it is simply short of air - Same basic procedure as above for a galvy tank only when it is completely devoid of water, test the existing air pressure with a tire gauge and add air (via the Schrader.tire valve) with a compressor or tire pump as needed. It should be set to the same pressure as the incoming water supply pressure to the house (So you will need to know/discover that one way or another - attach gauge to hose bib or similar). When done adding air (if any), open the water supply valve to the tank again.

    And/or it is also possible that the noises you hear are actually from the pipes rubbing the floor boards where they pass thru to the convectors. This also only be ascertained on site.

    It is also possible that the problem is caused by a faulty circulating valve which isn't opening properly at the appropriate time.

    I would check out the expansion tank and floorboards first and if that doesn't correct it or explain it, then you'll have to start looking deeper into things such as a faulty circulating valve. Do you have more than one heating zone involved? If so, you may be able to determine if this noise happens no matter which zone is calling for heat or whether it only happens when a particular zone calls for heat. If the latter, the circulating valve for that zone (or its relay controls) becomes suspect....in my mind anyway.
    Last edited by goldhiller; 11-09-2008 at 03:17 PM.

  6. #6
    Join Date
    Jan 2008
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    731

    Default Re: Banging pipes

    not that long ago the current season of Ask This Old House was a show where a homeowner had loud bangs and clanks when the system was warming up in the morning. in that show they traced it to copper pipes expanding and they installed isolation things they called mickeys to stop the noises.

    here is a link to the show description, it is about half or more down on the page. http://www.thisoldhouse.com/toh/tv/a...228407,00.html

    maybe you can catch the show in reruns cause i recall he covered some diagnosing tips before he decided it was the pipes moving causing the noises.

  7. #7
    Join Date
    Oct 2008
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    Smile Re: Banging pipes

    thanks for the extensive replies and the suggestions about the episode on TOH. BTW it is a hot water system, and I've bled the radiators. I have gone down to the cellar when the banging was going on and the noise does not get louder or seem to come from any part of the boiler so I doubt if it is the expansion tank. I am a home owner but would not take this on myself but after buying a new circulator perhaps unnecessarily last year I want to be as informed as possible when I call the oil company. I am assuming the "plumbing" part of my oil company is recommended rather than a "Official plumber"?

    I rather suspect it could be the floorboards but with a 1911 house, it wouldn't have copper pipes would it?

    Anyway at least I feel better informed than I did. Thanks for the response.

  8. #8
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    Jan 2008
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    Default Re: Banging pipes

    Quote Originally Posted by Mezsop View Post
    Hi,

    I know that I asked a questions about banging pipes where I received many good suggestions. I wanted to follow up since the problem was pretty much resolved. The service guy from the Oil Company came a couple of days ago. I felt well armed with info from this thread. However the problem seemed to be with the aquastat being set too high. The water was boiling away quickly in the pipe leading from the burner (causing the banging in the pipes). This never occured to me since there had been a service call for the burner check up earlier in the fall. He turned town the aquastat and watched while the heat came up until he was convinced that it would not be too low to heat the house. And although I can hear faint noises 90% of the clanging and banging has subsided.
    Thanks for the update.

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