Occasional bang in pipes

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jjspena

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I have had this ongoing issue that has been happening since we moved into our town home a little over a year ago. I am in the HVAC field so I have some working knowledge of plumbing but this one has me scratching my head. My water pressure coming in used to be around 95 psi so I installed a PRV and an expansion tank on the cold line right above the WH then set my pressure and EX tank to 62 psi. The issue still is that I am still hearing an occasional bang, sometimes about 5 or 6 with in an hour for maybe an hour or two, when nothing is using water. Most of the time it tends to start a few minutes after water has been used and is now off. I have checked all my flappers, have even turned off all toilets, and ran test but still getting noise. My theory was that when the electric water heater was heating that it was creating expansion and movement but then I quickly remembered that I have an expansion tank. Please, some one help me on this one because it is beyond my expertise for sure!
 

Bluebinky

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Is it a loud bang that shakes the walls, or more of a pop or snap type sound? You might be hearing a pipe rubbing (possibly binding a little) against a framing member or something as it expands and contracts with temperature. Does this happen more with hot water usage?
 

jjspena

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Is it a loud bang that shakes the walls, or more of a pop or snap type sound? You might be hearing a pipe rubbing (possibly binding a little) against a framing member or something as it expands and contracts with temperature. Does this happen more with hot water usage?


It does seem like it happens more often after the use of hot water but the walls do not shake. It is actually hard for me to pinpoint the spot when it occurs, as a matter of fact I believe the sound will come from a couple different spots. The sound is almost like a quick thud, kind of deep, and some louder than others. yeah, maybe like a pop or snap. It will sometimes occur 15 0r 20 min after water has been used
 

jjspena

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I have heard the thud about 6 times now as I was writing reply. It seems to be worse in the last few days. Wouldn't the expansion tank that I installed soften the blow? I don't understand why it seems worse now that I have an EX tank
 

Terry

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If you have used hot water, they can warm the waste lines, and they become larger and longer.
As they cool and contract, they can make noises in the wall as they slip back to their orginal sizing.
That happens most often if the holes are tight and a bit crooked where the pipe passes through the wood.
 

jjspena

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If you have used hot water, they can warm the waste lines, and they become larger and longer.
As they cool and contract, they can make noises in the wall as they slip back to their orginal sizing.
That happens most often if the holes are tight and a bit crooked where the pipe passes through the wood.

well the house is about 18 years old with the original cpvc and pvc lines which have not busted yet, but I am wondering if what you described will cause a major problem one day soon or if I should just move on and deal with the noises
 

Jadnashua

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Most house settling occurs in the first year or so after being built. But, something could have caused things to move a bit. You might check to see if there was a minor earthquake about the time you noticed this starting or a major storm with lots of rain that may have caused some settling of the house. That could have made changed things.
 
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