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Thread: Loud bang noise in the basement after flushing the toilet

  1. #1
    DIY Junior Member ovexi's Avatar
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    Default Loud bang noise in the basement after flushing the toilet

    After I flush the toilet and the water went down the drain, a few moments later I hear a loud banging noise from the basement. I did some reading and it is suggested that I may have a water hammer. However the water hammer is normally associated with a closing valve which is not the case here. The toilet valve closes after the tank is full. I am thinking that it may be related to the drainage pipe rather that the water supply pipe.
    Thank you for any help.

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    DIY Senior Member Mike Swearingen's Avatar
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    To determine whether it's the toilet supply line or the drain line, simply turn off the water to the toilet and flush it to see if the banging noise happens.
    Then you'll know what to look for to solve it. My guess is the supply line and you need to replace the toilet water inlet valve in the tank, as well as secure the supply line in the basement better. If so, I would go with a Fluidmaster 400A float-cup type tank valve. They're inexpensive (less than $10 bucks) and are easy to install. Just follow the illustrated installation directions that come with it.
    Good Luck!
    Mike

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    DIY Junior Member ovexi's Avatar
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    Thank you Mike. I checked the toilet (shut off the valve before flushing) and I still get the bang. Now, I notice the bang on the other toilet on the same floor and also banging noises (not as loud) when the tap water is running on the sink beside the toilet. drain problem maybe? I am planning to climb on the roof and check the drain exhaust, maybe it's clogged.

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    DIY Senior Member Mike Swearingen's Avatar
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    I don't think that it is a clogged vent. If a drain vent were clogged, it would be siphoning trap water out, allowing sewer gas back into the house, and you would be noticing that more than any banging.
    Have you been down in the basement and had someone try to get it to bang while you're searching for it down there? If you find a loose drain pipe and secure it better, that may solve the problem.
    Mike

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Is it a single bang or a bang-bang-bang? Sharp bang or more of a thump? Whatever you find, be sure to let us know...

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    DIY Junior Member ovexi's Avatar
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    I hear only one loud bang right after all the water went down the drain. I suspect it's the drain pipe down in the basement. The noise is happening before the valve closes so it is not likely water hammer. Also the other toilet on the same floor makes the same noise and I noticed some not as load bang noises when the sink water in running.

  7. #7

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    Dumb question: Do you have a sewage ejector pump or does your drain exit the house with gravity only? Check valves on sewage ejectors are notorious for banging shut after expulsion.

    Perhaps it's the sound of the angry woodpecker sitting on yr roof banging on yr vent pipe.
    (important note: I'm not a pro)

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    DIY Junior Member ovexi's Avatar
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    prashster, I have no idea how the sewage pipe looks like in the basement. What makes the diagnose even harder is that the basement is finished so I may have to break the wall in order to see what's going on there.

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    DIY Senior Member Mike Swearingen's Avatar
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    Don't be breaking into any walls yet, until you locate your problem.
    You should have a clean-out access somewhere that you can run a plumber's snake through down the drainline.
    Mike

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Can you even begin to guess what the layout of the waste piping is? I'm wondering if maybe there's a large verticle drop to a lateral line that might not be well-secured to the house structure. If a slug of water (1.6 gallons weighs about 13 pounds) were to hit that pipe after falling a ways, it might bang as it knocked against a framing member.

    An experienced plumber could probably make a good guess as to where things go by looking at the bathrooms' layout. Better yet, can you get the as-built plans from your local building department or the builder?

    If you could locate the cleanout, it would likely be on the inward end of any such lateral line, and close to the vertical pipe. Rest your hand on it while your lovely assistant flushes a toilet and see if you can feel any motion.

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    Licensed Grump GrumpyPlumber's Avatar
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    I'm making an educated guess from whats been said so far...
    The 3" (maybe 4") waste main is missing a support at one point, when the weight of water/drainage passes it drops and hits framing or drywall at the vertical drop.
    This would explain the sink making less noise than toilets.

    One possible quick fix would be to locate its position, drill a small hole and spray foam insulation directly under it...NOT the crack filling type...the large space foam insulation.
    The stuff dries pretty solid, would at least stop the movement, but not a real solution to a lack of supports.

    My other theory, a long lost ghost who gets angry when you flush and knocks on the ceiling to protest.
    "The biggest regrets we have in life are the chances we never took."

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    I like that theory. Do we know how old the house is? Maybe one of those chintzy steel strap hangers finally rusted out and the main is now hanging loose.

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    DIY Junior Member ovexi's Avatar
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    Quote Originally Posted by Mikey View Post
    I like that theory. Do we know how old the house is? Maybe one of those chintzy steel strap hangers finally rusted out and the main is now hanging loose.
    The house is 20 years old. Is it an emergency repair required guys? Is the pipe strong enough? The house is due for sale in a couple of months and I am thinking seriously if I really want to break the wall.

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    I'd do whatever I had to do to fix it. Fixed now, it might be a small repair, maybe only a few bucks plus the wall work. If a main sewer line is in fact hanging loose, it could fail eventually and result in an expensive and very messy repair. I don't know if this is a "material" issue that must be disclosed on sale -- check with your lawyer -- but if it were to fail shortly after the sale and the buyer were to read this thread I'll bet a beer you'd be on the hook.

  15. #15

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    It sure sounds like a sewage sump in the basement to me. Banging even when the water is shut off is a good indication. It's either that, or a drain is next to a structural member and the moving water is shifting the drain enough to hit something.

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