# Pipe knocking when toilet flushed



## BASSMASTER (Feb 18, 2006)

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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## mjdonovan (Mar 15, 2007)

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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## Termite (Apr 13, 2008)

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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## plumcass (Sep 27, 2008)

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.


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## napper (Jul 12, 2008)

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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