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 Posted: Wed Nov 5th, 2008 08:10 pm
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Roberta
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Okay here is my problem.. When any toilet in my house is flushed or the water fills the washing machine(cold water) the water heater heater goes THUMP. It is VERY loud. This has been happening for a year and 2 plumbers and another website can't tell me why. I thought it might be water hammer in the pipes but the noise is actually coming from the water heater,not the toilets or washer themselves. I was planning on turning off the main and letting the water drain from the faucets. But I just remembered this all started about the same time I had a plumber here to fix a leak and he turned off the water main at the street, then he(I think) let some air out of the water heater from on top. He said that since there would be air in the water lines there would be too much air in the tank. Nobody else had ever done that so am I right to think this could be related? How can I fix this?

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 Posted: Thu Nov 6th, 2008 01:30 am
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Ej
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A service call I once went on had the same problem that you described.  A thump in the water heater when you flushed the toilets.  The water heater acted as a sound chamber amplifying the sound.  You would be amazed at all the things water heaters get blamed for.  Anyway, I finally found that one of the toilets had a valve that closed very rapidly when the toilet filled.  Replacing the valve solved this problem.  Maybe try shutting off the individual supplies of the suspected faucets/toilets and operate one at a time until you find which one is causing the thump. 

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 Posted: Thu Nov 6th, 2008 06:45 am
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eleent
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Hello:  Two other considerations...  If the thump happens when water is first run, lowering pressure in the tank, it may be sediment in the tank has trapped some very hot water at the bottom of the (gas) heater and it flashes to steam on lowered pressure.  If the thump happens when water flow to the toilet stops, water hammer may be the difficulty.  Slow down the flow of water to the toilets and that will get rid of the hammer (or install a water hammer arrestor at each toilet).  I would get a gauge also and check water pressure, both static and when water is running. You don't want to see anything over 80 psi; 50 to 60 is best.  Do let us know what you find.  Hope it's not ghosts :shock:

Yours,  Larry

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 Posted: Sat Dec 12th, 2009 03:01 am
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Austin8034
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I am having a similar problem.  There is a loud thump coming from the (gas) water heater when our kitchen faucet or washing machine is turned on, or toilet on the other side of the wall from the water heater is flushed.  It doesn't happen every time, and since it happens when water is turned on, I'm guessing it's not water hammer (could it be?).  I flushed the water heater and didn't see any sediment wash out, so I'm not sure it's sediment buildup in the bottom of the WH.  Could there be larger chunks of sediment buildup that won't flush out?  Why would this even happen when cold water is turned on - there shouldn't be any flow through the WH, right?  Any help would be greatly appreciated - I'm at wit's end.  (WH is about 12 years old). Thanks!

Last edited on Sat Dec 12th, 2009 03:03 am by Austin8034

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 Posted: Sat Dec 12th, 2009 06:55 am
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eleent
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Hello:  Wit's end isn't such an unpleasant place :cool:  ...  Try this test.  When the heater has just finished firing, turn off the cold supply to the heater and run hot water at a tap.  Do you get the noise?  Do you get the noise if the heater has not recently been firing? If you had a pressure gauge, I'd have you put it on the drain valve of the heater and run cold water to see if pressure in the heater falls off with any water use.  If it does, it suggests poor flow in the supply to the house.   Clear as mud?

Yours,  Larry

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 Posted: Sat Dec 12th, 2009 08:48 pm
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Austin8034
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Thanks Larry, I'll try that "test" and see what happens.  I do suspect some issues with water flow to the house.  Many times when turning on a faucet or the clothes washer, there is a "surge" in pressure, which quickly tapers off to normal flow/pressure.  When this happens is when we usually hear the "thump" from the WH.  We've also had to replace the cartridge in our kitchen faucet twice in the past year (after it went the 6 years on the original cartridge), so I'm wondering if that is a related problem.

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 Posted: Sun Dec 13th, 2009 05:32 pm
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eleent
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Hello:  It might be worth the effort to buy or borrow a gauge (about $15).  I suspect you're experiencing a combination of high pressure and flow restriction.  Do let us know what you find :)

Yours,  Larry

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 Posted: Sat Dec 19th, 2009 06:41 pm
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Austin8034
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OK, I connected a pressure gauge to the drain valve, and here's what I found (I smell a rat):

- Steady state (no faucets, burner off):  70-72 psi (also 68-72 psi at garden hose faucet)
- Kitchen faucet on (cold or hot) or toilet re-filling:  45 psi
- Steady state with burner on (no faucets):  160+ psi !!!(had to shut the drain valve off since my gauge maxes out at 160 psi).
- Burner on, faucet on:  45 psi

Considering a nearly 120 psi pressure drop when a faucet is turned on while the burner is on or soon after the burner shuts off, I suspect this is the cause of the thump.  I've also been paying more attention to exactly when it is happening, and it is usually after we've used a lot of hot water (washing dishes, clothes, or shower), when the burner likely either on or just finished re-heating the tank.

So, what does this mean?  Is it a faulty pressure relief valve or some check valve at the WH or upstream?  What can I do?  Install a pressure relief tank?

Any help is greatly appreciated.

Thanks,
Dave

UPDATE:  After seeing 160 psi pressure in my WH I made a beeline to the plumbing supply store to buy an expansion tank.  Plumbed it in this afternoon and now when the WH is firing, pressure doesn't get above 72 psi, and so far, no more thumping.  Now my only concern is the pressure relief valve - seems like it should have opened before 160 psi.  Also not sure what was actually causing the thump - possibly the cold supply pipe in the tank?

Thanks for the suggestions of things to check!
 

Last edited on Sun Dec 20th, 2009 03:39 am by Austin8034

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