Hearing knocking noise when hot water is running... | TigerDroppings.com

Posted byMessage
Chicken
USA Fan
Jackassistan
Member since Aug 2003
6792 posts

Hearing knocking noise when hot water is running...


In the last few months, I have noticed a knocking sound when an upstairs water supply is running (it doesn't happen when downstairs water is running). Today, I narrowed it down to it just happening when hot water is running. I hear a single knock every 4 seconds. I don't hear the noise when just cold water is running.

I did some research and learned about "water hammer" but one site mentioned that this doesn't occur when water is running.

Anyhow, just wanted to bounce this off my OT brothers and sisters before I get a plumber out here.



This post was edited on 2/24 at 10:02 am



Back to top
Share:
NOBODY
Xavier Fan
Member since May 2007
48772 posts

re: Hearing knocking noise when hot water is running...


Are the pipes cold when this happens?


ETA:
quote:

I have noticed a knocking sound when an upstairs water supply is running.



BALLIN'






Back to top
Gorilla Ball
LSU Fan
Red Stick
Member since Feb 2006
2390 posts

re: Hearing knocking noise when hot water is running...


i think it means that there is air in the lines.





Back to top
real
LSU Fan
Dixieland
Member since Oct 2007
12718 posts

re: Hearing knocking noise when hot water is running...


I think g-ball has it right. Its air in ur line.





Back to top
Pigskin75
LSU Fan
Baton Rouge, La.
Member since Dec 2007
902 posts

re: Hearing knocking noise when hot water is running...


Water hammer would usually occur when you turn the flow off. Those extensions you see on some waterlines that come to a dead end are there to cushion the water flow against the trapped air in the extension. Over time that extension can loose the air cushion which would result in water hammer.

Water Hammer Wiki

Note the air chamber in the photo. That provides the cushion. Shut the water off to the house, drain the system, then turn the water on. Might fix you up.







Back to top
BallyHOO
Belmont Fan
Member since Oct 2005
6633 posts

re: Hearing knocking noise when hot water is running...


Is it pex?

The H2O line may be looses and knocking back and forth in the wall or attic.






Back to top
Chicken
USA Fan
Jackassistan
Member since Aug 2003
6792 posts

re: Hearing knocking noise when hot water is running...


Not sure if it is air since it is a single knock every 4 seconds...doesn't air make repeated knocks, like a machine gun going off?





Back to top
chip207
LSU Fan
Bossier Parish
Member since Feb 2007
4992 posts

re: Hearing knocking noise when hot water is running...


Look in the owners manual of your hot water heater it will tell you how to bleed the line.





Back to top
Chicken
USA Fan
Jackassistan
Member since Aug 2003
6792 posts

re: Hearing knocking noise when hot water is running...


Pigskin, it only happens when the water is running...thoughts?





Back to top
real
LSU Fan
Dixieland
Member since Oct 2007
12718 posts

re: Hearing knocking noise when hot water is running...


I beleive it could still be air coming through. Can you feel air pressure coming out when it makes the noise.Just a liitle pulse?





Back to top
Pigskin75
LSU Fan
Baton Rouge, La.
Member since Dec 2007
902 posts

re: Hearing knocking noise when hot water is running...


quote:

Pigskin, it only happens when the water is running...thoughts?


In that case you could have a good flow of water but the pipe is not secure. If you have an older home the line could be run on top of the rafters in the attic, like my home, and the flow could cause the pipe to move. If it can move enough, it could knock.

Does the noise come from a wall or the attic?






Back to top
Pigskin75
LSU Fan
Baton Rouge, La.
Member since Dec 2007
902 posts

re: Hearing knocking noise when hot water is running...


Think this one might nail it Chicken...

Water pipe knock

Date: 3/19/2005
Subject: Water Pipe Knock

Question
I get a knock in my hot water pipes. I have been underneath the house and the pipes are not knocking against the joist or any thing. The knock happens when I turn the hot water on. It also happens at times with the water off and I am walking across the kitchen floor. The hot water heater was replaced recently and it did before and after the heater replacement. Any ideas? Thanks.

Answer
Hi Elton,
Sounds like you may have water hammer. Back in the 60's we were required to to put shock absorbers,(air chambers) on all bath lavatorys and kitchen sinks. Over time water and condensate built up in them and they must be recharged. First turn off the house at the main house shut off valve. Then open hot and cold faucets at the farthest bathroom to prevent air lock.(This is importent.) You will find under each fixture little brass or chrome valves. These are called angle stops. With a small pail held under the angle stop to catch the run off look under the handle of the stop and you will see a nut with the stem running through it. This is called the bonnet packing nut. Put your wrench on it and back it off counterclockwise. Now open the stop and remove the stem and washer assembly, The stop will begain to drain. When it has quit draining reassemble the stop and move on to the next one. Do this on each one of your angle stops. There will be six of them. When you are done, close off the faucets you have opened, turn on the water to the house, and give yourself a pat on the back.
You have just recharged your air chambers and saved yourself a hefty service call bill. Hope this helps and thank you for rating my reply. TOM






Back to top
Helo
LSU Fan
Orlando
Member since Nov 2004
3609 posts

re: Hearing knocking noise when hot water is running...


I get this when I run hot water in my kitchen or when the dishwasher is running (or draining water). I don't think it is the water pipe since I recently changed all the piping in my house to Pex and it still does it. I think it has to do with the exhaust pipe which runs up the wall. Possibly the hot water is causing expanding or hot gases to make the knocking.





Back to top
lsu_tiger_az
LSU Fan
AZ/LA
Member since Mar 2004
30404 posts

re: Hearing knocking noise when hot water is running...


quote:

Anyhow, just wanted to bounce this off my OT brothers and sisters before I get a plumber out here.




Did you check the fetzer valve?








Back to top
Chicken
USA Fan
Jackassistan
Member since Aug 2003
6792 posts

re: Hearing knocking noise when hot water is running...


I just determined that I only hear it when the main shower in running...you can hear it in the floor of the closet that is adjacent to the shower.





Back to top
Chicken
USA Fan
Jackassistan
Member since Aug 2003
6792 posts

re: Hearing knocking noise when hot water is running...


quote:

I think it has to do with the exhaust pipe which runs up the wall. Possibly the hot water is causing expanding or hot gases to make the knocking.
Are you planning to have this fixed? I would be curious to know if this solved the issue...






Back to top
Chicken
USA Fan
Jackassistan
Member since Aug 2003
6792 posts

re: Hearing knocking noise when hot water is running...


quote:

Did you check the fetzer valve?
mother f#$%#er...






Back to top
Pigskin75
LSU Fan
Baton Rouge, La.
Member since Dec 2007
902 posts

re: Hearing knocking noise when hot water is running...


quote:

I just determined that I only hear it when the main shower in running...you can hear it in the floor of the closet that is adjacent to the shower.


It could just be expansion of the line then. As the hot water is running the pipe expands just a bit.

"When a draw is made on a hot water line the line expands against a pipe strap next to a stud and when you drain hot water from your tub or shower it goes into a chase that is a little cooler then room temperature. The heat expands the pipe causing it to rub against the stud to which it is pipe strapped. This is the sound you hear. As it cools it contracts and the noise is heard again. To repair it you must tear open the walls and locate the pipe strap that's causing the problem and shim it tight." LINK






Back to top
TigerLicks
Buffalo Fan
Dallas, TX
Member since Oct 2003
10695 posts

re: Hearing knocking noise when hot water is running...


Here's an answer from someone with the same problem:

LINK

Here's one for hot water:

quote:

Sometimes the knocking radiates along hot water pipes from a sediment-laden water heater that is in need of a good flushing.


You can attach a hose to your water heater, turn it on, and let it flush. I did that once, but the drain got stuck on, and I had to call in the plumber. Upstairs is the most likely spot for sediment/air to move in the lines.






Back to top
Chicken
USA Fan
Jackassistan
Member since Aug 2003
6792 posts

re: Hearing knocking noise when hot water is running...


quote:

To repair it you must tear open the walls and locate the pipe strap that's causing the problem and shim it tight."
I was afraid of that...






Back to top


Back to top