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#3119723 - 09/09/13 04:16 PM Resonance in the water heater every shut off
PandaBear Offline


Registered: 08/05/02
Posts: 12276
Loc: Silicon Valley
Gradually in the last several months, this sound gets louder and louder in the natural gas water heater if I shut off either / both hot and cold water anywhere inside the house, whether it is on a separate or mixed hot/cold water faucet or flush the toilet unless I shut it down so slow that it goes into a small stream / drip first.

I isolated the noise to the water heater, and have tried opening up the top valve to let out any possible air bubble, and it doesn't make any difference.

Has anyone seen this before? is it a sign of a dying water heater (made in 94, 50 gals for a 3 bedroom house), or something else?



Edited by PandaBear (09/09/13 04:18 PM)
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#3119735 - 09/09/13 04:26 PM Re: Resonance in the water heater every shut off [Re: PandaBear]
dishdude Offline


Registered: 11/14/08
Posts: 3213
Loc: Phoenix
I wonder if a piece of the anode rod broke off and is floating around inside?

I've never heard of this. It sounds like water hammer, but from inside the tank?

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#3119888 - 09/09/13 07:01 PM Re: Resonance in the water heater every shut off [Re: PandaBear]
hemitom Offline


Registered: 03/12/07
Posts: 730
Loc: canada
Sounds like pressure build up in the tank, maybe caused by sediment build (just a guess)


Edited by hemitom (09/09/13 07:02 PM)
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#3119916 - 09/09/13 07:16 PM Re: Resonance in the water heater every shut off [Re: PandaBear]
Eddie Offline


Registered: 12/07/03
Posts: 6588
Loc: Florida, Cape Coral
Most WH have a hose bib to flush out the tank every so often. If you have not flushed the tank, turn off the gas, connect a garden hose to the water bib and flush it out. It may not help if you haven't maintained it by flushing but, it might help. Ed
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#3119927 - 09/09/13 07:25 PM Re: Resonance in the water heater every shut off [Re: PandaBear]
Pop_Rivit Offline


Registered: 02/09/08
Posts: 3387
Loc: Midwest
If it's a whistling sound, it's buildup reducing the diameter of the pipes as new water enters or existing water exits the tank. If there are valves above the tank, you can try opening and closing them several times to see if they're the cause. You might also try draining and refilling the tank, but chances are that's not going to help.

The reason it doesn't happen when you turn the water off slowly is because you're not calling for a lot of water all at once. Turning a faucet full on and full off makes for a higher demand, and just like when you pucker up and whistle, it creates a noise. And just like when you pucker up and whistle, if you blow slow and gentle you don't get much of a whistle, but when you blow with more force you get a louder whistle. The same idea applies to the whistling pipes.

It could either be inside the water heater or the supply lines to the water heater.

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#3120021 - 09/09/13 08:30 PM Re: Resonance in the water heater every shut off [Re: PandaBear]
JimPghPA Offline


Registered: 08/22/09
Posts: 2799
Loc: Pittsburgh,PA U.S.A.
I am not a plumber, but do you have an expansion tank anywhere on the lines of the water tank?

Resonance can show at one location, and while that device probably is at least part of the problem, it may be that other things mechanically connected to it can be part of the problem.

Sometimes if you put a piece of pipe with a cap on the end sticking up above the section in question so air gets trapped in that pipe allowing it to act as a mini expansion tank, it can help get rid of any water hammer, or water vibrations.

Like I said, "I am not a plumber".

Just some thoughts on some things I would try if I had that problem.
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#3120145 - 09/10/13 02:26 AM Re: Resonance in the water heater every shut off [Re: PandaBear]
PandaBear Offline


Registered: 08/05/02
Posts: 12276
Loc: Silicon Valley
It definitely does not sound like a piece of hard object floating around and hit something. I have flushed the tank recently and the bib seal went bad, so I took the whole bib out to fix it. A lot of crud came out, probably was never flushed since it was installed, and a round plastic ball the size of marble 1/2" dia came out too. I was wondering if it was part of a check valve corroded away.

The sound is like a car tire thumping with a cupped tire, like a very low base from a woofer that has a harmonic twice to four times a second, and it last about 1 sec.
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#3120349 - 09/10/13 09:52 AM Re: Resonance in the water heater every shut off [Re: PandaBear]
Pop_Rivit Offline


Registered: 02/09/08
Posts: 3387
Loc: Midwest
Thumping or grumbling is an entirely different sound. Those noises are caused by water bubbling through the crud and sediment. Since a "lot of crud" came out when you drained the water heater, it's a safe bet that your water heater is pretty well coated on the inside with sediment and other crud.

It's not harmful other than it will reduce the lifespan of your water heater.

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#3120399 - 09/10/13 10:41 AM Re: Resonance in the water heater every shut off [Re: PandaBear]
dishdude Offline


Registered: 11/14/08
Posts: 3213
Loc: Phoenix
At almost 20 years old, it's at the end of it's life. I'd start shopping for a replacement now before it fails.

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#3120643 - 09/10/13 03:11 PM Re: Resonance in the water heater every shut off [Re: Pop_Rivit]
PandaBear Offline


Registered: 08/05/02
Posts: 12276
Loc: Silicon Valley
Originally Posted By: Pop_Rivit
Thumping or grumbling is an entirely different sound. Those noises are caused by water bubbling through the crud and sediment. Since a "lot of crud" came out when you drained the water heater, it's a safe bet that your water heater is pretty well coated on the inside with sediment and other crud.

It's not harmful other than it will reduce the lifespan of your water heater.


When I open the bib to drain, not much crud came out other than some sand, but when the bib seal failed and I took it out to "fix" it, that's when a lot of crud that resemble crushed oyster shell came out. Most of them a white and the size of steel cut oatmeal, some of them resemble a corner cut out of a dice with English letter (from the muni water?), and even a round plastic marble ball came out.

That's when the resonance / hum / voomimg sound when shutting off started.
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#3120671 - 09/10/13 03:39 PM Re: Resonance in the water heater every shut off [Re: PandaBear]
PandaBear Offline


Registered: 08/05/02
Posts: 12276
Loc: Silicon Valley
I think what I'm hearing is the "water hammer"
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#3120679 - 09/10/13 03:54 PM Re: Resonance in the water heater every shut off [Re: PandaBear]
dishdude Offline


Registered: 11/14/08
Posts: 3213
Loc: Phoenix

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#3120727 - 09/10/13 05:06 PM Re: Resonance in the water heater every shut off [Re: PandaBear]
SHOZ Offline


Registered: 06/28/03
Posts: 1539
Loc: Illinois
Bet the down pipe inside the tank has a reduced internal diameter due to being limed up.

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