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Completely renovated a new home recently. We always had issues with the water pressure, so the builder put in a new line from the city (1.5 inch) down a long driveway. We also got a tankless water heater (Navien NPE-210A).

Testing the cold water pressure I get about 100 psi, but as soon as anyone opens up a tap it drops to about 40 psi. After turning the tap off, it slowly climbs back up. I know the tankless water heater has a recirculation feature, but I turned the water off to it to do this test and it didn't make a difference.

The issue is turning on two taps of cold water drops the pressure even lower, making it impossible for more than one person to take a shower at a time. Any ideas of what to test or fix?

  • What is the change in grade? Or how high above the supply point are you , without this ??? – Ed Beal Nov 15 '19 at 1:08
  • How many bends, constrictions and elbows are between the incoming supply pipe and the taps you use? All these add losses which reduce the flow rate. – Solar Mike Nov 15 '19 at 14:18
  • if what you say is true, you have a pressure regulator or back flow preventer restricting flow. Even if the pressure regulator is not reducing pressure, it still can be a decent restriction although I don't think any one would cause what you describe. It could also be your water meter restricting flow. – ron Apr 13 at 18:28
  • find a way to fill a 5 gal bucket outdoors from a point nearest your water meter to rule out piping in your home. report back how long it takes u to fill a 5 gal bucket. If you have an outdoor faucet fill directly from faucet with it completely open, and also trace your piping back from it to your water meter accounting for any valves or other devices in that flow path – ron Apr 13 at 18:30
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Wow.. 1.5 inch should be adequate for an extremely long driveway!

I assume you're monitoring the pressure near where the supply pipe enters the home. If so, I'd try testing the pressure (with water flowing) as near to the customer side of the water meter as possible. That'll immediately reveal whether the flow restriction is in your piping or in the city's system (or meter).

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