Pressure issue that just cropped up

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Jim Dean

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Cumming, Georgia
Out of the blue I've got a bang in the cold water pipe. No plumbing changes or other issues, it just started banging. It bangs when the tub fill or any high volume use is on, and really bangs when any automatic valve, (toilet fill, dishwasher, washing machine) is functioning. As they cut on and off, it's a very audible bang.

I had loaned my good ol' pressure gauge out, so I went and bought one and stuck it on the back hose bibb, which I know is connected to the main house supply and is run though the pressure reducing valve.

I put a camera on it so I can see it from anywhere inside, and found a couple of things:
1-Very oddly, the banging is reduced. Somehow opening the inside shutoff to that valve (it was still off from winter) changed something. The dishwasher and tub no longer bang, but the washing machine does.

2-The pressure readings are concerning. It's showing a flat 120 PSI with nothing running. As soon as I crack a faucet, it drops all the way to 20 to 30 PSI. As soon as I kill the flow, it jumps right back up to 120. When I run the clothes washer, and it bangs, it drops to 20 and oscillates between 20 and 40.

I have not touched the pressure regulator yet to see if changing an adjustment will do anything-mine's a bear to get at. I figured I'd step in here and see if anyone else had seen one fail like this, or has any thoughts on the matter.



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Sounds like both a bad PRV and a bad thermal expansion tank. I am not a pro.
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