Loud bang noise in the basement after flushing the toilet

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by ovexi, Jan 7, 2008.

  1. ovexi

    ovexi New Member

    Messages:
    5
    Location:
    Canada
    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.
  2. 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
  3. ovexi

    ovexi New Member

    Messages:
    5
    Location:
    Canada
    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.
  4. 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
  5. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,736
    Location:
    Central Florida
    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...
  6. ovexi

    ovexi New Member

    Messages:
    5
    Location:
    Canada
    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. prashster

    prashster New Member

    Messages:
    941
    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.
  8. ovexi

    ovexi New Member

    Messages:
    5
    Location:
    Canada
    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.
  9. 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
  10. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,736
    Location:
    Central Florida
    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.
  11. GrumpyPlumber

    GrumpyPlumber Licensed Grump

    Messages:
    1,404
    Location:
    Licensed Grump
    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.
  12. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,736
    Location:
    Central Florida
    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.
  13. ovexi

    ovexi New Member

    Messages:
    5
    Location:
    Canada
    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.
  14. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,736
    Location:
    Central Florida
    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. Herk

    Herk Plumber

    Messages:
    547
    Location:
    S.E. Idaho
    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.
  16. pete11179

    pete11179 New Member

    Messages:
    1
    Location:
    Alberta Canada
    frustrated

    I am currently dealing with the same issue I have a 2 story home built in 2005 the main bath on the second floor toilet will bang in the basement when flushed the ensuite also on the second floor does the same but the main level half bath does not do it i have had 3 plubers look at the problem one talked about the hole "water hammer" thing i have drain all water from the pipes several times and refilled very slowly with no change, the second thought it was the pipes themselves said they were cheap material brought in the third said pipes were fine and the normal quality found in all new construction we opened 2 walls and found that the main stack had several broken ties almost 15 feet unsuported tied them in and after tested several times seemed fine again drained all water and refilled system to make sure still seemed ok put walls back together and it has just recently started again not nearly as bad but is now acompanied by a strange girgeling from the bath tub drain on main bath second floor. i have had all pipes scoped and all vent stacks inspected and could not find any problems the banging is significantly less but still present i have now spent 2000 and it really doesn't seem to be fixed . did u ever find any solution to your problem ?
  17. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    I would put my $ on a loose drain line inside the walls some where rather then a sewage pump, because why would a fixture on the top floor be draining into a sewage pump? Does the sewer enter the house in the attic or what. Not only that but he's never said once he even has a sewage pump in the basement.

    Not only that but at sewage pump wouldn't turn on after EVERY toilet flush.
    Last edited: Oct 16, 2010
  18. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,230
    Location:
    Cave Creek, Arizona
    Bangs in drain lines are either a pump check valve, or possibly a backwater valve in the main line. IF you cannot tell what is happening, call a plumber before you do ANY invasive diagnostics.
  19. turbocruiser

    turbocruiser New Member

    Messages:
    28
    Location:
    Colorado USA
    I always respond to threads with my whole "I'm no expert" bit but I had the exact same sound which was much worse with toilet flushes than with anything else even the full tub draining down. I did several specific things that helped. First I added additional "straps" to the drain lines down below the first floor. Instead of metal strapping I used plastic strapping which I think also helped soften the sound transmission. Then wherever I was able I took expanding foam and squirted it around the complete circumference of the drains that passed through joists, studs, subfloors, trusses etc. This was all made much easier because I basically removed several sections of drywall to replace the polybutylene plumbing the house had originally. After the foam fully dried I carefully cut it even with every penetration just to make the replacement of drywall easier. After I did that the toilet was super stealthy. I concur with the others' opinions that when you flush a fast 13 to 32 or more pounds of water all at once and it slams into something like a turn in the drain, it jars the drain thus causing the crashing sound. I don't think the drain lines would have ever had a problem but the sound was sort of troubling to me. Anyways, this "fix" really fixed the problem permanently. Hope this helps.
  20. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    If you can get the pipe to bang reliably, with an assistant listening and feeling you might be able to find exactly where in the wall the restraint is needed.
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