Hello there,


I have recently started hearing a knocking sound that seems to be originating from the wall/pipes near my water heater the moment I turn on the hot or warm water in any faucet in the house. The sound never occurs when only the cold water is turned on.


If the hot or warm water is turned on just slightly (low or medium flow) there is a continuous knocking until the water is shut off. However, when the hot or warm water is turned on all the way (high flow), there is only a single knock and then the sound stops.


To make things more interesting, there may also be a few times (4-5 times) throughout the day when I'll hear a single (slightly softer) similar knock even when no water is turned on.


Tracing the knocking sound, I have noticed that it seems to be coming from the pipe that runs OUT from the mixing valve on my water heater - and not the hot or cold water pipes running IN to the mixing valve. On a side note: The original mixing valve was faulty and had to be replaced over 6 months ago. However, there had been no issues with noise following replacement until just recently.


I've already tried clearing out the air in the pipes several times but the noise is still there.
From what I've read,symptoms don't seem to indicate a water hammer issue either (no sound when shutting off water.
It's the middle of summer so I'm assuming the pipes are pretty warm to begin with, so I figured thermal expansion is probably not an issue either.
I'm at a loss for what could be causing this noise and figured I would ask for some help and cross my fingers.
Hopefully Ive provided enough information to help diagnose the issue.
Thanks in advance for any advice/help!

What is a "mixing valve" on the water heater ? Please, be more specific, or, post photo of it if possible.

Thermal expansion comes to mind. Sound will travel so water heater may sound like an amplifier for the noise. See if the hot water pipe is not in tight hole ( like penetrating concrete or beam ) or too tight penetrating framing.

Have you tried removing the "mixing valve" and run hot water without it ?
If the noise began after you replaced the mixing valve than I would concentrate on the valve itself. Make sure that valve is installed as per manufacturer's instructions. Also, this valve could have Back Flow Preventer built that could be the source of noise. Check for any loose parts inside the mixing valve, too.

Back to you

Milo

Thank you for your quick reply Milo.A mixing valve helps prevent scalding and allows you to increase your available hot water supply by mixing hot water with cold. A lot of new water heaters come with it.Heres a diagram of one: http://waterheatertimer.org/images/Mixing-valve-16.jpg
(http://waterheatertimer.org/images/Mixing-valve-16.jpgWouldn't)
Wouldn't thermal expansion be an issue only if the air temperature or the pipes are cold (in the winter) and all of a sudden become hot when hot water is turned on?
The weather here is hot and pipes are already pretty warm to begin with. I would think thermal expansion wouldn't be an issue during summer.
I had a plumber install the mixing valve so I would have to ask him to remove it. I guess it could be an issue with the valve, as you mentioned. But it's a new valve and was installed 6 months ago and there have been no problems until now.
Thank you again!
Allen

The link shows "Not Available"

Yes, I am aware of "mixing valves" but not installed at hot water heaters. Usually, these are part of the faucet itself

Thermal expansion still could be the problem as water heater produces hot water at much higher temperature than temperature in your attic.

But with this mixing valve, I would definitely look at the installation of that valve, first

Let me know how it went

Milo

Thank you Milo,I will do as you suggested and have someone take a look at the mixing valve first.I will post an update as soon as I figure this out.Thanks again!

Thank you Milo,

I will do as you recommended and have a plumber take a look at the mixing valve first and see if that is the problem.
I will let you know how it goes.

Thanks again!

Is this the sites you referenced?

Water Heater Timers Save Money (http://out.easycounter.com/external/waterheatertimer.org)

I agree with the thermal expansion is causing the knocking sound, so check your hot water temperature settings and relief valve according to your site. Great idea to call the installing plumber back, and letting him know you have this issue.

I am with thermal expansion too. Have someone else turn on the hot water while you hold the hot water pipe with a gloved hand about 4' after the pipe leaves the heater. If it is expansion you will actually feel a small jolt in the pipe. If this is what you feel get back to us.

Thanks to all for your replies!
I have turned down the hot water temperature setting significantly but the knocking sound is still there.
I did also grab the pipe and I do feel a very small vibration in the pipe.Out of curiousity, if it is thermal expansion, why would I all of a sudden be experiencing it now? The pipes are the same since they were installed and have not been touched or changed in the past ten years and I've never had a problem until now?

Here is the link that I originally pasted:

http://waterheatertimer.org/images/Mixing-valve-16.jpg



(http://waterheatertimer.org/images/Mixing-valve-16.jpgThe)The other thing I noticed is that if I turn on the hot water fully at the faucet it only causes one knock and then it stops, but turning it on just slightly will cause a continuous knocking until the faucet is shut off.

Thanks to all!