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I have a plumbing issue that I'm looking for suggestions on. After using a substantial amount of hot water (say, a long shower + washing laundry) I will hear a loud rumbling / vibrating sound throughout the house, emanating from the water pipes. The noise seems to originate from the pressure regulator on the main water supply. If I open a hot water tap while the noise is occurring it will immediately stop. (The meters show that no water is flowing while the noise is occurring.)

I suspect that thermal expansion of hot water is causing backpressure on the regulator, and the noise is vibration as the seals in the regulator have water pushed past them.

My current plan is to get a pressure gauge and replicate the issue by nearly-emptying the hot water tank and letting it fill and heat. This should allow me to see the pressure swing in the system. Then based on what I see for the low and high pressures, consider the following options:

  • Decrease overall water pressure in the house so post-thermal-expansion it does not push back through the regulator.
  • Decrease hot water heater temperature (it's now around the recommended maximum of 130F-ish) to decrease thermal expansion.
  • Add an expansion tank to the hot side of the heater.

Does it sound like I'm on the right track?

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    Not a plumber, but it sounds right. In the meantime, though, I'd check your hot water heater's pressure relief valve; it should compensate for exactly this, and if it's locked up things could get entertaining quickly. – Daniel Griscom Mar 18 '16 at 18:52
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    The expansion tank should be on the cold water line just before it enters the hot water tank. If you don't already have one installed, that's the first thing I'd try. – Tester101 Mar 18 '16 at 22:46
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Now that you've confirmed it's nothing to do with the T&P valve or Water Heater & only to do with the Pressure Regulator. Then, definitely play with the Pressure Regulator's adjustment when it happens again. But, if the Pressure Regulator is acting up or not working normally, then order a rebuild kit & rebuild it.

  • Thank you for the comments, but the T&P valve is not the problem. With a gauge in place the pressure varies between 60 PSI and 40 PSI, well below the threshold for the valve. At this point I'm thinking that the house pressure begins to exceed the street pressure and the noise happens. I'm just waiting for it to happen again so I can see the gauge and figure out what's up. – Steve Vigneau Mar 21 '16 at 1:34
  • Ah, that is useful & I'm very glad to hear you checked the tank's pressure. However, how would the house create an over-pressure if it's not from the water Heater? If that's the case then I'd definitely still go with adjusting the valve up as it's happening to see if that removes it & proves your point & mine that the valve needs re-building. – Iggy Mar 21 '16 at 1:43
  • For now it's looking like the street pressure is varying enough that the regulator is keeping an overpressure in the house until something trips it to push back. I need to monitor it for a few days, but I think turning the regulator down will sort it out. Manually tripping the T&P won't do anything more than opening a faucet does: depressurize the system. It won't show if it needs rebuilding or not. (Unless it were to stick open or something...) – Steve Vigneau Mar 22 '16 at 2:28
  • Sorry, when I mentioned "valve" again I should've used "regulator". You should still look into re-building that since this is a new problem & the regulator may be showing its age. Definitely try turning the regulator down to see if a new equilibrium can be established. – Iggy Mar 22 '16 at 2:56
  • Ahh, got it. Thanks Iggy. Frustratingly, the issue hasn't occurred since I put the pressure gauge on the tank and slightly screwed with the regulator. :\ Looks like I need to just keep an eye on it... Or maybe there was some gunk in the regulator that a little screw-turning knocked free. – Steve Vigneau Mar 23 '16 at 14:43
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"Sounds" like bumping or boiling in a gas water heater. Sediment needs to be flushed from the heater.

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