Not your average hammer problem


Old 03-17-01, 11:25 AM
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Join Date: Feb 2001
Location: Seattle, WA
Posts: 664
I need a consult on this one. My client complains of an erratic woodpecker type water hammer noise coming from inside the walls between the first and second floors of the home. The home is aprox ten years old, copper piping, average construction, gas heat, gas HW, there is a PRV at the water meter set to 60 Psi. They say that the vibration happens at random intervals some mornings and on the weekends before noon. The noise has no correlation with water usage. The clients report that sometimes they lie in bed before they get up and hear the noise, which is loud enough to scare their dogs. I checked the PRV and it appears to be functioning normally at ranges from 20 to 80 Psi.
I wondered if the vibration could be caused by thermal expansion in the hot water system as they had no expansion tank. I could never duplicate the symptoms. I tried running individual fixtures and then I tried running all the fixtures. I ran out at least 50 Gal of hot water to test my theory but I never could make any noise happen. There appeared to be no back check valve on the main water supply but could the PRV act as a one way valve if the difference in the street pressure is dramatically higher? Could failure of the PRV be allowing massive pressure fluxuations? I installed a thermal expansion tank on the hot water system as my first and least invasive intervention but I have my fingers crossed that it will work. Anyone have a different take on this?
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Old 03-17-01, 10:11 PM
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Join Date: May 2000
Location: Eugene, Oregon
Posts: 5,841
With a PRV on the line, this is a closed system, sounds like thermo-expansion could be the cause, I have just replaced two prv valve due to failure, but I was able to tell they was bad do to excess pressure of 120 lbs at the hose bibbs, the thing about these prv's was the hammering that took place was only during use of hot or cold water, not just from the hot side. Replacement of these solved the problem.

If the expansion tank you installed does not solve the problem, then it could be the prv, I have a feeling the tank will solve this problem.

Let us know if it does or does not, I may have to deal with this problem in the future, and will like to know just what to do when that time comes.

Old 05-03-01, 09:05 PM
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Talking woodpecker you say?

I have the same problem. Mine turned out to be a real live red-headed woodpecker that likes to visit mornings before noon, weekdays and weekends. He lands on the top of the chimney and taps away at the aluminum cap. This echoes like mad down through the chimney and can be heard everywhere in the house. Sometimes he'll try the gutter instead. No doubt impressing the lady birds with the amount of noise he can make. Luckily I figured it out without having to pay a plumber...
Old 05-04-01, 07:24 AM
Join Date: Mar 2000
Location: Lake Murray, SC USA
Posts: 1,461
Welcome back Ron, we've missed you!

PaulyP, only thought I have is maybe they have a bad flapper valve and fill valve on one of the toilets, and they leak down enough to kick on at random times during the day. Of course you know to just valve off the toilets and see if the tank level water goes down.

Assume since the house is 10 years old, that the gas heat is forced warm air, and not water/radiators??
Old 05-04-01, 05:22 PM
Join Date: Dec 1999
Location: Northeastern NC On The Albemarle Sound
Posts: 10,952

WB, Buddy!
The D-I-Y Plumbing forum NEEDS your help.
I have probably screwed up half the plumbing in North America with my non-plumber advice. LOL.
Old 05-06-01, 12:09 AM
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Join Date: Feb 2001
Location: Seattle, WA
Posts: 664
Yes forced gas heat no radiant. I put in the expansion tank and never heard back from them. I am assuming that it worked. One of the other journeymen at the shop said that it was the bad flapper and a half closed angle stop scenario but I never had the chance to test that one out. Thanks for the advice everybody. This site is great!
Old 05-06-01, 08:44 AM
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Join Date: May 2000
Location: Eugene, Oregon
Posts: 5,841
A bad diaphram in one of those fill valves ball type can make racket if it's gone bad, but as you said it was random, and if it was the valve or stops, this could be duplicated.

You would have heard back from them if the expansion tank did not help.

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