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Old 10-10-2008, 04:34 AM   #1
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Water Hammer After Toilet Flush


Greetings Experts.
New home construction - after master toilet is flushed a "thunk,thunk,thunk" (3 times) water hammer noise is heard in the shower wall about 6 feet away. Flexible new water lines (not metal.) Can this be fixed without tearing open the wall? One estimater said to open wall and put in some kind of modulator. Thanks for your wisdom.

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Old 10-10-2008, 11:36 AM   #2
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Water Hammer After Toilet Flush


My guess is the sound you are hearing is a water hammer. The three in a row are caused by the sloshing of the water in the toilet tank as it nears being full. The water sloshes to one side and it shuts off, then sloshes to the other side and turns on, and the process repeats till the tank is over full or stops sloshing.

Since you have a new home do you have a warranty on it? If so this would be an item for them to fix.

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Old 10-10-2008, 11:43 AM   #3
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Water Hammer After Toilet Flush


Sounds like what you need is a water hammer arrestor.

http://www.plumbingsupply.com/waterhammerarresters.html

(I'm not recommending that web site to buy from, it's just the first thing to come up in google and includes an explanation of what it does..)

They show the arrestor(s) connected in a branch run, and those appear to be small units. My friend had the same problem and I installed a large arrestor near his HW heater (on the main supply), and it stopped the pipe noise in his house. I've heard of instances where this doesn't work though (maybe b/c plumbing runs are too long and the hammering is "localized").

This is a good description too, with a DIY approach: http://www.naturalhandyman.com/iip/i...infwatham.html

I personally wouldn't use an air chamber, because it will lose its effectiveness and need to be drained along with the system.
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Old 10-10-2008, 11:53 AM   #4
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Water Hammer After Toilet Flush


Quote:
The three in a row are caused by the sloshing of the water in the toilet tank as it nears being full. The water sloshes to one side and it shuts off, then sloshes to the other side and turns on, and the process repeats till the tank is over full or stops sloshing.
Our posts crossed, but that's a good point. I forgot about your 3-in-a-row.

Either way, a hammer arrestor should help.

(PS - Your water pressure also may be too high. That's a concern because it can wear out valves prematurely and cause other nasty problems. You can get a pressure gauge from Home Depot for less than 10 bucks and test. Your pressure should be around 60-80 psi. Much higher than 80 and you may want to look into a pressure reducing valve for the whole house. (About $60, I think).

I'm pointing this out because the higher the psi, the more severe and damaging the hammering can be. Not trying to scare you , high water pressure isn't the end of the world).
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Old 10-12-2008, 05:12 AM   #5
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Water Hammer After Toilet Flush


Gents - Thanks MUCH for your time and the good info. The latest: yes the warranty is being used with the builder ... the 3-thunk hammering happens as a result of the flush, but is in the wall about 10 feet away (after two 90 degree angle changes in walls) and behind the shower controls. The pipes are new flexible pipes and the plumber called out by the builder (could be in cahoots with the builder) said the water pressure is not too high (think I will check it myself, though) and he said we need a modulator in the pipes (open up the wall board to install) behind the shower control. He said that MIGHT stop the thumping. Apparently it is 3/4 inch pipe when it should have been 1/2 inch pipe (?). If I put a hammer arrestor on the toilet feed line I wonder if that will help even though the thumping/hammering noise is over 10 feet away in the wall pipes to the shower? If you have an further feedback, I welcome it. Have a great day.
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Old 10-12-2008, 09:28 AM   #6
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Water Hammer After Toilet Flush


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Originally Posted by Covey582 View Post
Gents - Thanks MUCH for your time and the good info. The latest: yes the warranty is being used with the builder ... the 3-thunk hammering happens as a result of the flush, but is in the wall about 10 feet away (after two 90 degree angle changes in walls) and behind the shower controls. The pipes are new flexible pipes and the plumber called out by the builder (could be in cahoots with the builder) said the water pressure is not too high (think I will check it myself, though) and he said we need a modulator in the pipes (open up the wall board to install) behind the shower control. He said that MIGHT stop the thumping. Apparently it is 3/4 inch pipe when it should have been 1/2 inch pipe (?). If I put a hammer arrestor on the toilet feed line I wonder if that will help even though the thumping/hammering noise is over 10 feet away in the wall pipes to the shower? If you have an further feedback, I welcome it. Have a great day.
Any where close to where the problem is will help. It doesn't have to be at the source. I have taken a length of pipe and ran it up the wall a foot or so. It had air in it and air will take the knock out most of the time.

It's a simple fix if it weren't for the fact that you have to open up a wall to do it.
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Old 10-12-2008, 12:06 PM   #7
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Thanks, M.G., I'll try to absorb the abrupt pressure change (extra pipe is a logical idea like the old air-pipes of pre-code days, I've read) and hope that takes care of the noise. This is a great site to let smarter people help people facing a new building challenge.
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Old 10-12-2008, 01:46 PM   #8
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Thanks, M.G., I'll try to absorb the abrupt pressure change (extra pipe is a logical idea like the old air-pipes of pre-code days, I've read) and hope that takes care of the noise. This is a great site to let smarter people help people facing a new building challenge.
Now the unwritten rule is that you have to tell us if the problem was solved and how you solved it. It helps me at least to be better at diagnosing problems and proposing remedies.

So you are on the hook now....advice does cost...just not a lot...
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Old 10-12-2008, 02:38 PM   #9
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Will Do ... it will take a few weeks as I am travelling but I'll report back.
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Old 11-10-2008, 04:03 AM   #10
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Water Hammer After Toilet Flush


Finally have an update for you all. I have decided to not install a hammer arrester at the toilet tank base, or in the wall . The noise has "moved" location in the wall and diminished. By turning the toilet intake water valve down to 1/3 open, the noise is gone. Tank fills a bit slower but not noticable unless you are into timing toilet tank fill times. In other words, valve position is now silencing the noise so we will live with it and monitor.
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Old 11-14-2012, 03:11 PM   #11
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Water Hammer After Toilet Flush


Try changing the shower cartrige if you have one. I spent over $600.00 in hammer arrestors,expansion tanks and a main water water regulator valve ,not to mention the walls and ceilings I opened to check the pipes.And I just replaced my shower single handle Delta anti scalding cartridge (part# RP19804) and my nightmare is over.I read this months ago on a blog but dissmisted it as my problem,I should have tried it then ,it would have saved me money and stress.Hope this helps.Paul
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Old 11-14-2012, 06:50 PM   #12
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Water Hammer After Toilet Flush


It sounds to me like the main culprit is that the flexible lines in the shower are not properly secured, so when there is a spike in pressure, the damn things hit the wall when they move around.

Closing the valve partway worked as you know by reducing the volume of water and so the violence of the movement. It's probably still moving but not enough to hit anything.

And if it keeps moving, it may, eventually cause a connection to fail in the wall.
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Old 11-15-2012, 02:25 PM   #13
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Water Hammer After Toilet Flush


The valve is back-seated so that top backseats against the bonnet. Leaving it in partial position can lead to a leak at the stem.
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Old 11-15-2012, 09:20 PM   #14
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Try changing the shower cartrige if you have one. I spent over $600.00 in hammer arrestors,expansion tanks and a main water water regulator valve ,not to mention the walls and ceilings I opened to check the pipes.And I just replaced my shower single handle Delta anti scalding cartridge (part# RP19804) and my nightmare is over.I read this months ago on a blog but dissmisted it as my problem,I should have tried it then ,it would have saved me money and stress.Hope this helps.Paul
Definately look into this.

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