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Old 02-23-2006, 01:48 PM   #1
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Pipe knocking when toilet flushed

I have an American Standard toilet on the second floor. Last year when I re-modeled the bathroom I replaced all of the internal parts with new. The Fill valve is now a Fluidmaster. When you flush the toilet you can hear the pipe knock or bang in the basement? If you flush the toilet while the toilet is still running it does not do it. If you depress the lever on top of the fill valve you can hear the pipe banging. I have installed an arrester just after the water shut off valve. It did not help. Does anyone have any suggestions as to how to fix the issue?:confused:


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Old 03-10-2006, 08:21 PM   #2
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I am by all means no plumber but, i'll take a crack at this.

the only thing I can think of is if you had your main water shut off at some point and when turned back on you have air in the lines.

Open all faucets in the house at the same time showers, tub etc. Flush all toilets with all faucets open, then shut thwem all off.

This may work. hopefully a real plumber will come along and give you real advise.


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Old 07-20-2008, 06:36 AM   #3
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I am not a plumber but it sounds like you may have air in your pipes. Also, sometimes when the float valve shuts off this sudden change in water flow can cause the pipes to bounce. You may want to make sure the supply line pipe in the basement that feeds this toilet is securely fastened to a wall stud.

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Old 07-20-2008, 09:32 AM   #4
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Fast acting valves can create water hammer. You did right by putting an arrestor in, as I assume that your suspicion was the same as mine.

I'd do what the previous post said and make sure that your pipes are all well-secured. Even with arrestors, you can still get some bounce somewhere else in the line.

My cold line jumps a little and makes a racket on the fill cycle when running a load of laundry. The washer is well over 30' from the location that the water hammer affects the pipe.
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Old 09-27-2008, 05:00 PM   #5
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A loose washer in the toilet supply line or fill valve would cause banging in pipes. If it happens when running other fixtures it could be a main line valve. The old globe valves with neoprene washers did this occasionally especially when turn off and on. Another thing to try (long shot) turn down the flow of water to the tank if there is a separate toilet valve.

Last edited by plumcass; 09-27-2008 at 05:04 PM. Reason: mispellings
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Old 09-27-2008, 08:17 PM   #6
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I agree with plumcass.

A lower flow will decrease the water hammer effect. Also this is not caused by air being in your system...it could actually be caused by not having enough air in your built in snubbers.


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