• How to test PRV failure

    How to test PRV failure

    Quick Answer:

    Measure static pressure with a gauge, then measure flowing pressure while the bathtub spout is running. Close the house shutoff and watch if the pressure holds to check for a leak. If the regulator won’t hold a setpoint or the setpoint drifts quickly after adjustment, the PRV is likely failing — but first rule out clogged aerators and partially closed valves.

    Why This Happens

    Pressure reducing valves (PRVs) wear, get stuck, or leak internally. Sediment and scale can prevent the valve seat from sealing or moving freely, or the internal spring can weaken. That produces unstable pressure at the house or low pressure under flow. Sometimes the apparent problem is not the valve at all — a partially closed meter or house shutoff, or a clogged faucet aerator, will mimic PRV trouble. If the valve is physically stuck by grit that’s sitting on the seat you may see the classic pattern of dropping pressure or intermittent recovery — think of a PRV clogged by sediment. In other cases the whole house has poor flow because the PRV is set wrong or failing, similar to a scenario where the regulator is the cause and the symptom reads like PRV causing low water pressure everywhere.

    Step-by-Step What to Do

    1. Prepare a pressure gauge

    • Use a simple water pressure gauge that screws onto an outdoor hose spigot or washing-machine cold inlet. These are inexpensive and give a clear reading in psi or bar.
    • Make sure no faucets or appliances are running inside the house before you take the first number.

    2. Record static pressure

    • With everything in the house off, attach the gauge and note the steady reading. This is the static pressure.
    • Write it down and the time — municipal pressure can vary throughout the day.

    3. Record flowing pressure at a tub spout

    • Start the main bathtub spout (full flow, ideally from the same plumbing branch you are testing). Then check the gauge on the outdoor spigot while the tub is running. The tub creates the flow condition; the gauge shows how much pressure remains under load.
    • Compare static vs flowing pressure. A small drop is normal; a large drop suggests a restriction or failing PRV.

    4. Rule out local restrictions

    • Remove faucet aerators and screen filters on fixtures that are slow and run the tests again — a blockage at an aerator can mimic PRV problems.
    • Check that individual fixture valves (and the house shutoff) are fully open. Partially closed valves at the meter or main will reduce pressure and flow.

    5. Leak check by closing the house main

    • With the gauge attached, close the inside house main shutoff valve (not the water company meter valve). Watch the pressure reading for 5–10 minutes.
    • If pressure falls slowly while the house main is closed, you have an interior leak. If it holds steady and the incoming supply is steady, there’s no large interior leak and the problem is more likely the PRV or supply side.

    6. Check PRV adjustment and setpoint stability

    • If the PRV has an adjustment screw or nut and is accessible, note the current setpoint and, if comfortable, make a small adjustment to change the setpoint a few psi. Watch the gauge over 10–20 minutes.
    • If the valve won’t change the pressure or it drifts back quickly to the old value, the PRV is not holding and is likely failing. At that point replacement is appropriate.
    • If you’re not comfortable adjusting the PRV, a professional can test and bench-check the valve instead.

    What Not to Do

    • Don’t replace PRV before ruling out partially closed meter/main valves.
    • Don’t assume the first symptom you see is the PRV — check aerators, fixture valves and for interior leaks first.
    • Don’t disassemble or repair the PRV unless you have experience; internal springs and seals are under water pressure and require proper reassembly.

    When to Call a Professional

    • Call a licensed plumber if the gauge shows unstable pressure after you’ve ruled out aerators, partially closed valves and interior leaks, or if the PRV won’t hold after you try a safe adjustment.
    • If your house pressure is very high (over 80–100 psi) call a pro immediately — high pressure can damage plumbing and appliances.
    • Ask a plumber to bench-test the PRV if you want a definitive diagnosis before buying a replacement valve.

    Safety Notes

    • When you run fixtures for testing, be careful with hot water — set cold-only when possible to avoid scalds.
    • Close only the interior house shutoff for the leak test; don’t tamper with the meter or the water company’s shutoff valve.
    • Relieve pressure before disconnecting any fittings and use proper tools. If you’re unsure, stop and call a plumber.

    Common Homeowner Questions

    • How much pressure drop is normal when a tub is running? A drop of 5–10 psi is common; larger drops suggest a restriction or failing PRV.
    • Can I adjust the PRV myself? You can make small adjustments to test stability, but if it won’t hold or you are unsure, hire a plumber.
    • How long does a PRV usually last? Many last 5–15 years depending on water quality; sediment shortens life.