I've been trying to track down water pressure/flow issues throughout the plumbing in my entire house, but haven't found anything which made any significant difference. For example, I discovered that the main valve and a few others were not fully open. I am able to access all other valves and they are fully open. All lines are copper. My house is a single level with a basement (where the main is located). My neighbors do not have any problems.

Here's my configuration:

City Water -> 3/4" lines -> main -> gauge (reading is maxed out over 100 psi) -> PRV -> gauge reading static 60 psi -> valve -> continue 3/4" lines feeding 1/2" lines for all fixtures.

I have a thermal expansion tank with the hot water heater which is also set to 60 psi.

As soon as any water fixture is turned on (sink, shower, toilet flush, washing machine, etc.), the pressure on gauge immediately following my PRV drops significantly (falls to 20psi or less). As a result, trying to use a second fixture is difficult and a third is near impossible. Additionally, I attempted to turn all water fixtures through the house on. During this test, the water fixtures on the main level did not put out any water.

I'm inclined to believe there is an issue with the PRV. Is that the right place to be looking? Should a PRV have such a large drop in pressure when one fixture is open?

  • My guess is that either the city's shutoff valve is not fully open, or there is an obstruction in the 3/4" line from the shutoff valve to your PRV. I'd think the former would be more likely, as the latter would mean something caused the obstruction (roots, collapse), which, one would think, would also cause a leak. The pressure should drop whenever any plumbing fixture is turned on (per Bernoulli), but going down to 20 PSI from 60 seems a bit excessive to me.
    – BillDOe
    Sep 26, 2015 at 17:16
  • If the pressure before the PRV is 100 psi, and the pressure after is 60 psi, then the valve seems to be working. When you open a valve so that water starts flowing, the pressure in the system will drop. Without seeing how your plumbing is set up, it's difficult to help you locate the problem. It sounds like you have a problem with the volume of water, not the pressure.
    – Tester101
    Sep 26, 2015 at 19:13
  • You said you live in a one story with a basement, and then said the fixtures on the "main" level did not put out water. How many fixtures are in the not main (basement?) level, and what type of fixtures?
    – Tester101
    Sep 26, 2015 at 19:16
  • Do the 1/2" lines feed more than one fixture per line?
    – Tester101
    Sep 26, 2015 at 19:35
  • @Tester101 Thanks for getting back to me. On the basement level, there is: a half bath with a sink and toilet (I opened the sink hot and cold a little) and flushed the toilet, a laundry tub (I opened the hot and cold a little) and the washing machine (I started a load of laundry).
    – srobb
    Sep 26, 2015 at 19:40

1 Answer 1


I replaced the PRV with an exact match and it fixed the issue. It was a fairly straight forward replacement since the PRV had one union and my backflow preventer (about 10" down the line) had another.

  • 1
    Can you open up the old PRV, and inspect the strainer? You might be able to see the deposits, if you look in the inlet side of the valve. I suspect that it may be blocked up with the same white-ish debris that was blocking up the faucets.
    – Tester101
    Oct 3, 2015 at 15:18

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