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- over 420,000 Posts - PlumbingForum.com -
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Author:
cmr_lsu (AL)
We have been hearing this knocking noise for about a month now. It happens at random time throughout the night and day. Nothing is running and there is no flow in toilets or sinks. My kitchen sink has developed a slight leak at the faucet. When the knocking occurs I started shutting valves. It stope when I shut the cold valve to the hot water heater and continues when I open it. I think that the thermal expansion tank has failed and it pushing water back through the Pressure Reducing Valve to the street. This is causing the water hammer (it has a destintive pattern every time - 20 secs with fast knocking at the end). If we open any faucet during the knocking, it stops (assumes this redirect pressure).
How can I tell the thermal expansion tank is bead (3 years old)? It is not leaking. I would think the Pressure reducing valve may have failed, but it never makes this sound when water is running. Any ideas on what this could be and how to fix it?
Thanks
Chris
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Author:
dlh (TX)
well, since it stops when you turn the water off to your water heater then i seriously doubt it is caused by a prv since that is usually on the main line before it goes to anything.
i would say it is either your pipes expanding as they heat or you have a bad washer/seal in a faucet somewhere
to check the expansion tank turn the water off and bleed the pressure off by opening a hot and a cold faucet. get a tire pressure gauge and check the air pressure in the tank. if it is more than a few pounds below the incoming water pressure from the street/well add air until it is 2 psi below incoming pressure and see if it holds if it doesnt then the tank is bad and needs to be replaced
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PLUMBERS "Protecting The Health Of The Nation"
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Author:
Shoemaker2 (MA)
You can tap on the tank and listen for ringing sound. If it rings it's ok, if it thuds it is bad. This would be the the air chuck end of tank.
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Author:
LemonPlumber (FL)
You either have a bad prv or your tet is bad.I am thinking the prv is bad!Shut off the water to your home.Open a few faucets.take a tire pressure gauge and test the tet .Is it is 30 to 50 or the factory setting?Pump it up if not, and see if it holds for a few minutes???
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Good Luck.Insulate your hot piping.
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Author:
maximumprojects (TX)
I recently watched an old episode of "This old house" the homeowners had the same problem which you describe and they installed a "anti-knocking" device which seemed to take care of the problem. It was installed in their basement which connected to the main water line, it involved some pipe cutting and some welding in 2 different areas but the problem was completely corrected.
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Author:
dlh (TX)
sometimes that does nothing but mask the problem. the problem could very well still exist after installing hammer arrestors and if it is a washer or something else it will get worse and could potentially become an even bigger problem.
the answer is to figure out what the actual problem is then fix it. a hammer arrestor may be the fix but i doubt it in this case
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PLUMBERS "Protecting The Health Of The Nation"
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