Water hammer correction (C) Carson Dunlop AssociatesWater Hammer Plumbing Noise FAQs
Diagnostic questions help find & fix the causes water hammer or shock - noisy pipes & fixtures

  • WATER HAMMER NOISE FAQs - CONTENTS: questions & answers about water hammer noise - also called "air hammer" noise in pipes, causes & cures for banging clanging pipes. These FAQs help diagnose & cure water supply & Drain Piping Noises and discuss sources of water hammer noise suppression devices.
  • POST a QUESTION or READ FAQs about banging pipes and water hammer noise: how to find, fix, or prevent banging water pipes or heating pipes

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Banging pipes & water hammer noise diagnosis, cure:

Water hammer noises in plumbing is also called hydrostatic shock. Our page top photo shows a water hammer noise suppression device produced by Oatey and available at building suppliers.

This particular water hammer noise suppressor is interesting because it's designed to be added to a hose bib or washing machine hose connection by a homeowner, avoiding having to cut and solder pipes.

The articles at this website will answer most questions about plumbing noise associated with water hammer or water surge, including the diagnosis and cure of water hammer noises as well as many other building plumbing system inspection or defect topics.

Green links show where you are. © Copyright 2017, All Rights Reserved.

Water Hammer Noises Diagnosis & Cure FAQs

Photograph of  this antiquated laundry sink with several unsanitary plumbing violations in view.Some of the banging pipe noise and water hammer FAQs discussed below are adapted from information provided by the Watts Regulator Company in a 1973 publication. - see REFERENCES.

Recently posted questions about water hammer and water hammer noise control, posted originally at WATER HAMMER NOISE DIAGNOSE & CURE

On 2017-04-03 by (mod) - can water hammer suppresors go bad or clog up?

AUTHOR:R.S. (no email)

Do hammer suppressors go bad OR do they get clogged up and stop working because of that?


A water hammer arrestor can be damaged by mis-handling during installation, as Watts points out in their installation guide.

But typical water hammer arrestor design includes a sealed chamber that should not clog nor fail by leakage.

If the water hammer arrestor never worked satisfactorily I suspect that it was installed in the wrong location or that the wrong size was selected.

Water hammer an occur on a plumbing system as a "new" issue also if / when any valve is changed to a different type, such as a fast-closing zone valve on a heating boiler.

On 2017-03-20 by (mod) re: hot water pressure loss and banging pipes

Searching InspectApedia using the search box just above and looking for "HOT WATER PRESSURE LOSS" finds this article that may help you diagnose the trouble you describe:

I think I'd start by looking for scale in the water heater or calorifier or geyser or hot water cylinder - depending on where you live.

On 2017-03-20 by Luis G.

I have pipe banging I lose pressure on the hot water I still have pressure in the cold water what can cause this

On 2017-02-17 by Mary

How do I fix the hammering on my water heater

On 2016-10-25 by (mod) re: night time knocknig noises

Bill, if you're sure this is a piping noise, yes the watering system could be the cause. See if the watering timer setting corresponds with the noise.

On 2016-10-16 by BIll

LOud knocks between 2am and 4|30am. NO inside or outside water is running at that time. Our home is on a water supply with 300 other homes. The water supply company has 3 wells in our community. DUring the day there is no knocking, thumping, sputtering of any kind. THe noise is on the side of the house with the meter.

Is pressure from water supply causing this when someone's irrigation, or swimming pool turns on, or flush of toilet from neighbor between the hours of 2am and 4:30am?

On 2016-10-25 by (mod) Banging Pipes in Ontario


Thank you for the nice comments. We work hard to provide authoritative, unbiased information, so we're thrilled when a reader finds useful.

We also welcome questions, content suggestions, and critique, so don't hesitate to ask. Working together makes us smarter.

On 2016-10-04 by David H. - a loud banging sound from the plumbing when they use the Guest washroom

We have a guest bathroom which is not all that frequently used. Recently friends from Poughkeepsie New York visited us here in Ontario. I was surprised to hear a loud banging sound from the plumbing when they use the Guest washroom.

This morning after their departure I reviewed this very helpful page and learned about the causes of this irritating hammer-like sound. Happily the solution was easy and one I learned about from this page. I adjusted the water flow by opening the water shut off to the side of the sink on the hot water side and the noise went away. Thank you very much! The next time my friends from Poughkeepsie visit I won't have to be embarrassed by my plumbing sounds. :-)

On 2016-05-24 by Rose - water heater makes a hammering noise

My hot water heater makes a hammering noise when I've done a few loads of laundry. What can the cause of this be? I still get hot water but the noise worries me.

On 2016-03-21 by (mod) re: my radiators are banging so loud that a pipe in the basement popped

Sure Antoine,

at the CONTINUE READING links just above see the live link for


to diagnose and repair this trouble. Usuallly the problem in your case is condensate is not returning.

On 2016-03-21 by Antoine

my radiators are banging so loud that a pipe in the basement popped. i sealed it temporarily with a screw. i located a leak , due to the radiator not being tightened of the small pressure valves in the basement is leaking water at the part where only steam is supposed to come out.i am so done... help me please.

On 2016-01-21 by (mod) re: i installed my water arrester at the pressurize tank.


It may be that the installation location you chose is not the best - see the notes above about locating near highest fixture.

On 2016-01-21 by robert

i installed my water arrester at the pressurize tank. Our water source is an overhead tank, water pump is located lower than the source and check valve next and pressurize tank after..... but hammering still exist and annoying every time the pressure switch shut-off. please give me more details location of tapping the said device. thanks

On 2016-01-16 by (mod) re: noise like something falling in the wall

Perhaps cooling metal ductwork

On 2016-01-16 by Rosie

A noise that sounds like something falling in the wall when the heat turns on or off?

On 2015-11-13 by (mod) re: violent radiator hammer sounds in my building apartment

Search inspectapedia for

banging radiator noise

For some suggestions you can share with the building owner.

On 2015-11-13 19:46:50.722183 by Robert F

I live in Plymouth Wisconsin. Are you aware of, or can you direct me to, a website/phone number which will help address violent radiator hammer sounds in my building apartment? I have approached the building manager and landlord to address/repair the problem and they have been dismissive.
Do I have any recourse other than treating this as tenant vs. landlord legal matter?
Thank you.
Robert F

On 2015-11-08 15:33:26.517660 by Andy

Thanks. I'll give it a try.

On 2015-11-08 by (mod) re: where to install the water hammer arrestor.

I'm over my head here Andy and uncertain between following the mfg's generic instructions - which places the arrester ahead of the highest fixture - and your observation that you find the hammer occurring near the point of water entry; from your description it seems reasonable to install the water hammer arrestor ahead of the booster pump.

And you'll be conducting some water hammer science: do let me know if that does the trick.

On 2015-11-07 by Andy

Follow up on Reader Question: where to install the water hammer arrestor.

Thank you for your advice. Regarding the size of the arrestor, there is really only a single device: the booster.

The main line into the house goes directly to the pressure regulator/booster pump, and then on to all of the "fixtures" in the house. Since the hammer appears to be between the main shutoff valve on the supply side to the house and the regulator, would this be considered "one fixture", or should I attempt to cover all of the fixtures in the house past the booster pump? Thanks again.

Question: How to Identify Water Hammer Noise in Buildings

(Apr 25, 2015) Chad said:
While water is running through the shower, I suddenly have the water shut off, and there is loud banging in the walls. After reviewing multiple posts, I have not see that others are havinng issues with the water shutting off. Would this still be considered water hammer, or something else?

(July 3, 2014) Krystyl Cruz said: when I flush the toilet there is a loud sound like a jackhammer

When I flush the toilet, a few seconds later (when the water is refilling) a loud sound like a jack hammer comes from the wall behind the toilet. Sometimes if I turn the faucet on in the sink the banging will stop, but if I turn the faucet back off the banging starts again until the toilet stops running.

(Mar 1, 2015) D said:
When turning off hot water I hear a banging

(June 9, 2015) Anonymous said:
When toilet is flushed or cold water is run there is a loud noise which goes away when the hot/cold water taps are run. This only happens in warm weather.

(Sept 10, 2015) Robin said:
When I turn my bathroom faucet on, the pipes start clattering. It mostly does it when I turn the hot water on. Could this be caused by dirty inlets in the faucet? I didn't have this problem until the plumber installed a new hot water tank.

Reply: the above are all examples of water hammer noise

Thanks for the questions, Chad, Krystyl and D and others. If the water flow stops, that is a separate problem from the loud banging. I'd guess that the banging is indeed water hammer - which can occur when water supply shuts off suddenly in a piping system. But the banging is not likely to itself be the *cause* of the sudden loss of water. That sounds more as if a valve is closing.

You are almost certainly describing a water hammer problem. I've found just the symptoms you describe including that opening a faucet, because it changes the flow rate and pressure in the piping, can move the flow rate off of that speed that is causing the horrible banging sound.

Since water hammer is a feature of water flow velocity and is affected by loose pipes, or valves that close suddenly, I'd look in detail at exactly what has changed; try slight adjustments to water pressure.

Robin: Of course you'll want to clean out dirty faucet strainers but I doubt that's the source of trouble unless those conditions have changed the water flow rate. In fact water hammer is more likely to appear when water velocity is faster so cleaning out clogs may increase it.

Question: does water hammer in my plumbing system cause damage?

What effects can water hammer have on my house plumbing system? Other than making noise, does it actually hurt anything?


Water hammer causes a sudden "banging" of water supply piping that creates movement and stresses in the system, not just annoying noise.

Water hammer can cause loosening of water supply piping connections, leading to plumbing leaks and related damage

Watch out: Water hammer shocks to the water supply system are more serious at higher operating pressures. On hot water heaters the TP valve is usually set 20 to 30 psi above the anticipated maximum system water pressure. This is high enough that the relief valve won't leak or spill when water hammer occurs in thte system. But at higher water pressures, say 70 psi to 90 psi, the relief valve may be damaged or leak when water hammer occurs.

At our article on WATER PRESSURE REDUCER / REGULATOR you 'll see that we recommend against operating a home at pressures above 70 psi because of the increased risk of plumbing system or plumbing fixture leaks. [10] paraphrased

Question: can I record water hammer noise? Loud banging that isn't water hammering?

(Oct 27, 2011) Ian Anderson said:

Hello, is there sound recording equipment to prove water hammer noise from neighbours flat?

(Jan 15, 2012) Anonymous said:

Mike I have a 75 gallom power vent gas hwh the home is well water ther is a check valve on the cold water side of the hwh there is also a expanchion tank n both are between the ball valve and hwh i am getting alot of load banging on both the hot and cold side when water is running and it isnt water hammering because i put air aresters on system its happening when both cold and hot are running I was wondering if it was the check valve causeing the banging sound ?


Ian, you can use any recording equipment, even a sound recorder on a cell phone to record the sounds you describe. I've done that with great success. If you are using a cell phone hold it against a noisy wall or ceiling for strongest sound transmission into the device.

Anon: Putting air arresters onto the system may not have been enough to cure the water hammer if they were too small in capacity.

Question: loud hammering noise wakes me up

(June 21, 2012) jt said:

I am hearing loud hammerins noises, loud enough to wake me up, in the middle of the night. It sounds like the tap is being turned off and on but this is not the case.
When I do use the tap, it only makes the banging noise if I turn it on and off very sharply.
What can I do?


JT, if the loud hammering noises are in the water supply piping, it seems most likely that someone is turning water on and off, or a well pump is turning on and off on its own - if you have a well pump try checking out causes of the well pump "turning on by itself".

Securing loose piping and installing a water hammer control device (described in the article above can also help stop the problem.

Question: various banging, moaning, clanging plumbing noise complaints

(Sept 2, 2012) Tom said:

The noise is not as much about banging but a loud moan in the hot water line between the washing machine and the Master bath tub supply, although if you flush the toilet the noise stops until the tank is filled.

Have tried everything from turning off the water and draining all the lines and refilling each line in different sequences, nothing works?

(Jan 4, 2013) Ted L. said:

Thermal Expansion: When water is heated in the Water Heater it causes water to expand thus an increase in water pressure.

A Code requirement and solution is to install an Expansion tank on the cold water supply line ahead of the Water Heater. The rubber gland will absorb the expanded water and release it when a tap is opened. Expansion problems prevail when no water is being used and the tank is heating.

(Jan 19, 2013) Gary S. said:

I live in a 37 unit appartment and at nightime I can hear a low pounding noise in the distant Would this noise affect the heat temp in my unit. I have hydronic heating.

(Feb 25, 2013) Ykip said:

I experience a severe water hammer when turning on and off the bathtub spout. How can I fix the water hammer arrestor on it? It seems impossible. The water pressure to the house is normal and about 70psi. I appreciate anyone to help me. Thanks,

Question: Rumbing pipes under the toilet

(Mar 5, 2014) Help! said:

My house pipes seem to rumble under the toilet. The toilet is upstairs
I have a water tank in the loft and also a water tank in a cupboard upstairs.

The time does not appear to be defined by any one event (the heating coming on, the water heater turning on, washing machine going).
However this rumbling also sometimes goes 'off' if you sit on the toilet or simply walk into the bathroom.

The times are also intermittent. Sometimes it doesnt rumble at all, sometimes once every hour, sometimes every few hours or sometimes every 20 minutes (which drives me mad!)
But the 'rumble' does cease when the toilet is flushed (for a time)?

I am not in any way DIY minded so do not feel comfortable investigating the problem myself.
However wondered if you could perhaps assist in telling me what it is and assumedly i need to get a plumber - how much it would potentially cost to fix?



This rumbling doesn't sound like water hammer. Water hammer is a percussive "BANG!" that or maybe "BANG BANG bang clank" short duration clamor that occurs when water is running (fast and at high pressure and flow rate) and then is suddenly shut off.

If it's not a coincidence, sitting on the toilet or walking into the bathroom wouldn't be expected to impact a water hammer problem so I suspect we're looking for something else.

Let's start by trying to isolate systems to find out which system is responsible. I suspect we're looking at something related to heating, not water supply, or a water heater.

Water heaters that have formed a scale deposit on the heater bottom will often make an ongoing rumbling popping sort of sound * when the heater is operating * that is, when it's heat source is on.

So when you hear the noise let's notice what systems are running and which are off.

Or you could turn off the water heater for say half a day and see if the noise abates.

Search InspectApedia for "Water Heater Scale" to read more about this hypothesis.

Keep us posted and we'll pursue it.

Question: water pressure booster pump noise

(Mar 9, 2014) Anonymous said:

water pressure booster pump noise going through my water pipes what can I do?


If th problem is not a banging when water is turne off in the building then I guess you refer to the transmission of noise from the pump motor. You'll want to look at sound-isolating fixtures to isolate the vibrating piping from the building structure. Regular pipe hangers won't do it.


(Apr 3, 2014) ron said:

at our cottage the water system was fine. its a submerable pump with an air bleeder valve just before the electrical switch. its 25 yrs old. however it seams that when we replaced the tap in the shower the pipes started to shake and water spurts out. This happens after we have used the water system for a bit then it keeps banging/shaking/spurting. also when filling the toilet. thanks



It's not a complete surprise; sometimes when we simply change the water flow rate we change the vibration behaviour of the system.

It might be diagnostic to open a tap when you hear the banging water hammer noise. Openign a tap elsewhere changes the pressure and flow in the system.

I'd also double check that nothing has changed on the water supply end.

Let me know what you find.

Question: banging noise in pipes at night, 3-5 seconds apart, 7-8 bangs

(Apr 3, 2014) Dave said:

My question is this. At night i am hearing a banging in the pipes every 3-5 seconds of approximately 7-8 bangs. They can be felt when touching the pipes from the laundry room. They are not overly loud. The seem to go away for a brief time when I run the water at the lowest faucet in the house. Any ideas?



You're probably describing water hammer as we discuss it above.

Question: trouble tracking down water hammer noise

(Apr 19, 2014) Lynn Pepe said:

For the past 5 days, we hear what sounds similar to water hammer, can not pinpoint where it is coming from. Tbis happens any time of day or night, does not seem to be related to turning water on or off. We have tried shutting down the main and running the water out several times. We have had the water company to check. what can this be???


Lynn, I would be just shooting in the dark to guess very specifically, but surely if you hear the sound when water into the building is shut off completely it's not a water supply system problem. At that point I'd be looking at hot water heating, steam heating piping, and if those are ruled out, I'd be looking for other sources of mechanical movement.

Question: will the Temperature & Pressure relief valve protect the hot water tank against water hammer damage?

Will the T&P valve protect the tank against breaking from excessive water hammer? - Watts


An "excessive" water hammer is an abnormal but momentary condition that causes a very brief surge in water system pressure. The pressure-relief component of a temperature and pressure relief valve can only discharge a verly limited amount of the surged pressure during the moment of shock of the water hammer event, possibly none.

If water hammer is causing frequent opening of the temperature and pressure relief valve there may also be a risk that the frequent passage of hot water through the valve deposits scale that eventually accumulates to a level at which it prevents safe reliable operation of the valve in an emergency.

And the fact that temperatures inside the hot water storage tank are elevated above cold water temperatures makes no difference - with the exception of the warning we issue next.

Watch out: if the hot water tank is in an abnormal overheated condition, that is water in the tank has become superheated above its atmospheric boiling point water hammer could actually lead to a water heater tank explosion. According to Watts Regulator Company, "Water hammer conditions are believed to be a partial factor in starting off an explosion of overheated tanks besides "pressure heat rupture". [10] paraphrased

Question: septic pump check valve noise

5/29/14 Naaj said:

Water-hammering noise from check valve in septic sump pump…solution?


Check that you don't have multiple check valves installed on the same piping system. If there is only one then you're ok on that score and you'll want to install an anti-water hammer noise product such as those discussed above.

Question: ball cock in the water tank in loft causeing water hammer

(Oct 18, 2014) mr conner said:

can it be the ball cock in the water tank in loft causeing water hammer


No, not directly but possibly indirectly:

Water hammer is an effect of the velocity of movement in water pipes along with pipe dimensions and layout, combined with a sudden STOP! of water flow. Any valve can "cause" the effect to be heard. Some plumbers install slow closing valves to reduce the problem but you'll read other solutions in the article above.

Question: banging pipe issues

(Nov 3, 2014) Hope said:

We recently had issues with banging pipes in our home. A plumber recently came out and replaced the water pressure regulator along with adding an expansion tank to our water heater but now after a month or so the noise is back and isn't happening when the water is running like it was before but when the water softner is running. Please help...what could the problem be now?



I'd like to help but with not a shred of information about your home, piping, water supply, pressure, valves, usage, etc. my best advice remains in the article above. If any part of that is unclear please just ask.

Question: banging pipes and water softeners

(Nov 18, 2014) A Kang said:

At my home (Cypress Texas), we hear water hammer noise at the end of water softner regeneration cycle. There was no water hammer prior to installation of water softner. I brought in the water softner installer and could not figure out why and told may be water pressure is high when the regeneration cycle occurs. He changed regeneration cycle time from night to afternoon and we still have water hammer.

The regeneration cycle is after 10 days and lasts for 1 hr 45 minutes. Did water softner not installed properly? The house was built in late 2010 (by village builders a subsidiary of Lennar Homes). We had water water softner installed in 9/2011. We purchased this new home and moved in April 2011. I called in a plumber and he was not much help. I am considering to contact the plumbing company (New Tex) who did the original plumbing in the home. May be they can figure out and fix this problem. Any guidance you have. Thanks



Ask about installing either an appropriate water hammer control device (described in the article above) or a slow-closing control valve on the supply to the water softener.

Question: why does water hammer noise suddenly appear in a building?

(Apr 12, 2015) Carl C said:
Why would my plumbing suddenly start making water hammer bangs when it never did before? Nothing changed in my plumbing or any appliances, yet I start hearing significant water hammer. Yesterday, all was quite as it has been for years, then today I hear water hammer. Any ideas?


Great question, Carl. I can speculate that

- water pressure may have increased at the source

- a pipe or fixture has come loose

- a control valve has been opened or closed to a different extent than previously

As water hammer is related in large part to velocity of flow and sudden stopping, a change in a valve can be enough. Certainly something has changed so let's start with that assumption.


(Apr 15, 2015) lose prime said:
Replaced pressure tank with bigger capacity tank. Water now loses prime every so often. Could it be the preassure switch or backflow valve got debris in it?



That's a smart guess, particularly if your water pump uses an internal check valve or if such a valve is installed at the pump, else I suspect a failing foot valve. I'm not clear why this is a water hammer noise question.

Question: water hammer noise after installing a booster pump for water pressure

2 Nov 2015 Andy said:

I've recently replaced a booster pump in my residence. This new pump switches on Immediately on noting a pressure drop (water being used) versus the old one which had a timer delay before powering on. I installed a Honeywell pressure reducer on the supply side of the pump and my total pressure is around 60. All should be good - but when water is used, there is quite a hammer going on.

The hammer appears to be on the supply side of the pressure reducer/pump (because I hear a copper bang) versus on the output side of the pump (house flow which is plastic).

I thought about maybe installing an arrestor, but since the hammer is on the supply side, I have no idea where to install it. I also find it odd that I have a hammer on the supply side.
Any advice would be appreciated. The pump vendor is suggesting a pressure tank on the output side, but until I understand what is going on, I don't want to start modifying plumbing. Thanks.


Interesting; Indeed I'd install a water hammer arrestor on the side of equipment, valve, or device where the hammering appears to occur; Anywhere close to that point should work.

Usually we install the water hammer arrestor between the shutoff valve and the incoming water supply line - close to the valve. Or we may need to install a water hammer arrestor on both hot and cold water piping systems. If that doesn't work for you I suspect the water hammer arrestor was not properly sized.

Here is what water hammer manufacturers say

"The location should be at the piping serving the fixture(s) and normally between the last two fixtures. " - J.R. Smith Manufacturing Co.

"Water hammer arresters shall be specifically sized and have sufficient volume of air to dissipate the calculated kinetic energy generated by closing residential or commercial faucets or valves. Arresters shall be installed on both hot and cold lines on the supply stops where applicable. Arresters shall be approved for installation with no access panel required." Sioux Chief Manufacturing Co.


Continue reading at WATER HAMMER NOISE DIAGNOSE & CURE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see these

Plumbing Noise Articles

Suggested citation for this web page

WATER HAMMER NOISE FAQs at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia

Or see


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher's Google+ Page by Daniel Friedman