Banging Pipes: A non-obvious source of banging in my pipes.

posted 1999-Dec-12
— updated 1999-Dec-13
Are your pipes banging?

(Boy, that sounds sexual, doesn't it? It isn't.)

For nearly a week last summer (maybe 5 days) I noticed a loud repetitive banging coming from the pipes in my house. I'd hear it in the basement, a single "bam!" every 5-10 minutes. I hadn't heard it before, and I was wondering what it was.

I was ready to dismiss it (although it's a little annoying if you're trying to read sitting in the living room, and your silence is periodically interrupted) as a common household noise, and assume it would go away.

But then I decided to search on the 'net, and the only references I could find to banging pipes was with steam-fed radiators [which, BTW, should not make that noise: word on the street is that it's indicative of a problem which needs to be fixed. I guess all that banging I used to hear on winter mornings in high-school could have been avoided.] and that banging in the pipes can be a rather damaging thing.

"Well, crap," said I. "What'll I do?"

For a couple of days I sat and worried about it, thinking of mailing everyone I knew who owned a house to see if they knew what it could be. I noticed that it was a little more frequent in the day than at night.

Magically, I suddenly realized what was causing it, fixed it, and it's all better!
Can you guess what the problem was?


I bought a bunch of fantastic little doo-dads which go on the ends of your hoses and watering paraphanelia, which not only make it easy to attach/unattach items (just push-them-together) but they also have valves in them to prevent the water from flowing unless it's hooked together. (This is FABULOUS! When you're done using the sprinkler, just unplug it from the hose, and the water stops flowing!) This leads to us sometimes forgetting to turn off the spigot. (When all is well, there are no leaks, so I figured this was no problem.)

However, the hose was lying there, in the sun, heating up, attached and open to the house water supply, and I guess the valves were occasionally releasing a bit of pressure and WHAM water would go into/out of the house.

I wanted to let you all put this piece of knowledge in your brains in case something similar occurs to you.

Aaron de Chazal
09:22PM ET

Indeed, the phenomenon is called "water hammer". As you correctly ascertained it occurs when a water source is shut off rapidly like with single handle kitchen faucets, dishwasher or washing machine valves etc.

Nowadays it is plumbing code to make strategically placed hammer arrestors consisting of a foot or so of supply plumbing running straight up then being capped, thereby permanently trapping some air in your water line. Then when a valve is shut off quickly, the incompressible fluid has a shock cusion rather than banging the pipes. Water hammer is most common in older houses that were built before rapid valve actuation appliances were readily used. That or your plumber didn't guess that you'd leave the hose outside in the sun with a leaky shutoff valve.

Preparing to build my own house has filled me with many fun and useless house facts.

Kai Bau-Madsen
05:43AM ET
Hey chaps,

Interesting indeed. I've been mulling over a similar household problem here. My heating system (which is a natural gas system) burbles. I'm guessing it's a low water problem, the pressure being insufficient and inconsistent, allowing air into the pipes and then forcing it back through. Wouldn't mention this, but Chazal seems to have a real grasp on plumbing and such. Cheers guys.
12:36PM ET
I also have a loud bang in my pipes but not when I shut the water off. It occurs about 8 seconds after I have turned the hot water on which is gas heated and occurs when any faucet is turned on. I have been informed that this is not water hammer because it doesn't happen when the water is shut off. It sounds like an elephant has hit the pipes. Any ideas?
Aaron de Chazal
01:11PM ET
Leesalou, I also have this phenomenon in my house when the hot water is turned on. In my case the bang comes from the copper hot water supply pipe expanding axially in the direction of the pipe. You'll typically get this when you have a long hot water run and the pipe is semi-rigidly fastened to the bottom of a series of floor joists. Plumbers often us "V" shaped hangers (they look like they are made from coat hanger wire) to hang supply lines, when the pipe expands lengthwise, the V naturally tightens... to a point, then "POP" it releases. No damage done but it's annoying. The first thing is to locate the troublesome section of pipe, then look at the hangers/fasteners used. You can reshape the V to more of a U which allows freedom of expansion or change to a different hanger type. In your case since it happens when any faucet is turned on, I'd guess you need to look at one of the hot water supply lines that is common to all affected faucets.
12:30PM ET
I just recently have the noise when I turn the hot water tap in the kitchen, It will run for about 30 sec to a minute then makes the loud noise. I noticed that the noise also comes from the pipes in the wall behind the washing machine which I prozume is the same hot water pipe
that feeds the kitchen faucet.
01:37PM ET
i have a 2 flat buiding that is a 100 years-old my tennat just recently informed that the pipes are knocking/banging i have a hot water system i tried bleeding the radiators on both floors it onlybang 9pm 2 9am its not all the time it start and stop the funny thing about the whole thing the heat be off. please help
01:27PM ET
Our house is a new build. From the minute we moved in, the pipes in the house bang loudly. It happens when nobody is using any water, just bangs on and off all day long in the vacinity of the kitchen and half bath. I have had the plumbers here 4 times, and all they do is change some part in the downstairs toilet, which doesn't do anything to fix the problem. What can be causing this, and why can't the plumber see what it is? It's driving me crazy! Is there anything my husband can do to stop this terrible noise? Any help would be GREATLY appreciated! Thanks!
09:22PM ET
HELP!!! When we flush, run cold water or turn on the showers the pipes start ratteling in the walls. I have no idea what it is or how to stop it. I have already had one plumber ut and he well lets just say he didn't fix the problem. Anyone know what this is, I have read everyones statement about water hammer but it sounds like that happens after the water is off. Mine is while the water is running.
04:54AM ET
I have recently noticed a popping sound that lasts for approx 30 secs after turning off the HOT water only. It doesn't happen with cold. Any ideas?
06:00AM ET
the popping sound seems to be coming from the pipes and not the water heater, my house is 8 years old
10:54AM ET

I’ve looked this up on the internet, and the only references I can find are from issues associated with banging pipes when the water is turned on and then off quickly. I have a somewhat different problem. Because my water pump kicks on and off frequently when it is on, I shut off the main water supply (which keeps the pump from running all of the time), and only turn it on when we are showering, dishes, flushing, etc., until I can get it looked at. Problem: I am hearing frequent banging from the cellar even the I have the main water supply shut off, aand like I said, only turn it on when needed, then shut the main off again. If the main water supply is shut off for long periods of time, and only turned on when needing to use water, what is causing all of this banging in the pipes?

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