Old house, 1948, city water. I have regulator on main set to 50psi

We had a problem when washer runs it's impossible to take shower. But recently (last 3 month or so) it became worse. If you take shower and someone flushes toilet water flow in a shower almost goes to the 0.

I have central filter system, so I replaced filters at first, no help. Then I opened bypass valve (on filter which I have to temporary reroute cold when changing filter) - same thing.

Then I adjusted regulator to 70 psi. Now I get more pressure but once something else uses water - it drops. It almost feels like "not enough volume" if that is correct term.

It's not specific to any of the faucets, not specific to hot or cold. It almost feels like not enough "path through" for more than one recipient.

I ask neighbor and his pressure seem to be OK. He said maybe in a morning when people run sprinklers he would see lower pressures. But other than that - OK

When measuring and all recipient shut - 70psi When opening kitchen faucet - pressure drops to 40psi When washer filling up - pressure drops to 20psi

Any suggestions on what that should mean? Bad regulator? When washer running I can hear "hiss" where main comes in to house, so definitely some restriction going on.

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2 Answers 2


You should take some pressure readings upstream of your regulator. During use the regulator should continue to open to try to deliver at the set pressure, until it is wide open if necessary. If the pressure upstream shows a similar pressure drop during use, your problem is not the regulator.

You should also consider:

  • if you have recently had to shut off your water. Sometimes shutoff valves fail when they get old and do not completely open
  • if the city or water delivery entity has made changes or done any recent work
  • the type (e.g. PVC, copper, steel) of main water pipe you have, and the size of the main. Same for all the house piping. If there is old galvanized in the system...
  • Jimmy, That makes perfect sense. However, there is nowhere to take this reading. I have ranch and water comes into basement with 1 in galvanized pipe and then I have main. Everything after that is copper and about 1/2 of which was already replaced by me during remodels. So, everything downstream is in tip top shape. Shutoff - this is something. It is OLD, and yes, I recently closed it to install pressure tank, timing seem correct. I guess it's time to call a plumber to replace main as I have no means to shut off on a street. Hopefully street shut off actually works :(
    – katit
    May 30, 2020 at 18:29
  • Good news! Incoming pipe is copper. So, hopefully this is it. Pressure regulator when fails does not regulate, correct? It can't present flow problems itself and regulate top at the same time?
    – katit
    May 30, 2020 at 18:41
  • The pressure regulator can fail in different ways but by design they are supposed to "fail safe" i.e. fail to open. So... it could be the gate valve (if it truly is an old gate valve, this is a prime suspect,;it might only be partially open) or maybe the regulator. May 30, 2020 at 19:08
  • Ok. I will get main shutoff replaced. It's leaking and old. If it doesn't help I can always replace pressure regulator myself. But seeing how it was 50psi and it did follow adjustment to 70psi I doubt it's actually restricting flow. Not a big deal to replace later anyway (when I have good shut off)
    – katit
    May 31, 2020 at 2:38
  • Just a counterpoint: a pressure regulator can adjust from 50 to 70 psi. with barely a move when things are static; when you draw on the system the valve then must open up (perhaps all the way, depending on supply pressure and hydraulics) to attempt to maintain the setpoint pressure. May 31, 2020 at 4:55

You may have galvanized water piping in the house or between the street and the house. Over time these pipes corrode and the corrosion and collection of minerals makes the inside diameter of the pipes much smaller. This restricts the flow of water and would explain your issue. Sadly there is no good fix beyond having the piping replaced with modern copper or plastic. See this article, note the 5th paragraph describes your issue with the shower and washer exactly.

  • Well. "Main" is bad, it's leaking and needs to be replaced so I will start with this. Too bad can't DIY. But I will hope Jimmy's guess on bad main is what causing it..
    – katit
    May 30, 2020 at 18:32
  • I had galvanized pipes in my home, had the same problems. I had one of those "repiping" specialist companies come out and replace it with copper. They did the entire piping job in one day, we left for work and when we came home, it was done and the plumbing was working again. Then another day just to smooth the drywall patches and they were done. All of the pressure problems went away.
    – JRaef
    May 30, 2020 at 23:24

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