PRV stuck high causing pressure spikes

Pressure gauge showing sudden spikes from PRV

Quick Answer:

If your pressure gauge shows occasional spikes and you hear plumbing stress noises while the reducing valve seems to let pressure run high, first check static pressure by attaching a gauge to an outside hose bib, then run a tub spout to look for flowing spikes. Try a careful, small adjustment of the PRV while watching the gauge. If the valve will not regulate, plan to replace the PRV and verify the expansion tank isn’t waterlogged before reinstalling. If you see leaks or the valve fails to change pressure, call a pro.

Why This Happens

  • PRVs (pressure reducing valves) can stick due to mineral buildup, worn internal parts, or a failed spring and diaphragm. When they stick high the house sees pressure spikes under flow.
  • Pressure spikes can also be made worse if the expansion tank is waterlogged and can’t absorb thermal expansion from the water heater.
  • If the PRV can’t relieve or reduce pressure it may force the water heater’s relief valve to operate or cause other failures — this can show up as a continuously rising gauge or intermittent loud pipe noises. If you see overflow or dripping from the water heater relief, consult the note about PRV dripping at relief port.

Step-by-Step What to Do

1. Prepare and attach a pressure gauge to a hose bib for static pressure

  • Make sure no water is running inside the house (all faucets closed, dishwasher/washing machine idle).
  • Screw a pressure gauge onto an outdoor hose bib or other convenient spigot. Read and record the static pressure.

2. Run a tub spout and watch for flowing spikes

  • Open a tub spout to a steady flow and watch the gauge. Note any spikes above the normal setting (usually 50–60 psi for many homes).
  • If pressure jumps only when water flows, that indicates the PRV may not be reducing under dynamic conditions. If your gauge behavior is erratic around the PRV, see guidance under Pressure gauge readings unstable at PRV.

3. Attempt a controlled PRV adjustment

  • Locate the PRV on the main water line. Most have a locknut and an adjustment screw on top.
  • Loosen the locknut, then make very small adjustments (a quarter turn) on the adjustment screw. After each small turn, tighten the locknut, recheck static pressure, and test flow. Wait a minute between moves so the system stabilizes.
  • Lower pressure slowly and watch for changes. If the PRV does not move the pressure after a couple of cautious attempts, stop — continued forceful adjustment can damage the valve.

4. If the PRV won’t regulate, plan replacement and verify the expansion tank

  • If controlled adjustment doesn’t restore steady pressure, plan to replace the PRV. A failing PRV should be replaced rather than abused.
  • Before replacing, check the expansion tank: tap it (a hollow sound suggests air; a dull sound suggests waterlogged), and check its air precharge at the Schrader valve with a tire gauge. The tank pressure should be about 2 psi below your system’s static pressure (consult the tank sticker/manual for exact guidance).
  • If the tank is waterlogged or its precharge is wrong, drain or replace it per manufacturer instructions or have a pro handle it. A bad expansion tank can mimic or worsen PRV problems.
  • When ready to replace the PRV, shut off the main water supply, relieve downstream pressure, and either replace the valve yourself if competent or hire a licensed plumber.

What Not to Do

  • Don’t ignore spikes; they can rupture lines and damage water heater components.
  • Don’t make large, rapid turns on the PRV adjustment screw — use very small changes and monitor the gauge.
  • Don’t remove the PRV or work on the main without shutting off and relieving pressure; sudden pressurized discharge is dangerous.

When to Call a Professional

  • If the PRV won’t respond to careful adjustment or keeps drifting back to high pressure.
  • If you see water leaking from the water heater T&P (temperature/pressure) relief or repeated relief activation.
  • If the expansion tank is waterlogged and you’re unsure how to safely isolate, recharge, or replace it.
  • If you’re not comfortable shutting off the main, draining sections of the system, or soldering/working on pressurized piping — call a licensed plumber.

Safety Notes

  • Always depressurize and shut off the water before opening or removing a valve. Relieve downstream pressure by opening a faucet.
  • Wear eye protection when working on pressurized plumbing. Hot water can cause scalding.
  • If your water heater is gas-fired, do not alter gas or combustion components; call a professional for any water heater work you’re not trained to perform.
  • Follow manufacturer instructions for any replacement parts. Incorrect installation of a PRV can create unsafe system pressure conditions.

Common Homeowner Questions

  • How high is too high for home water pressure?
    Consistently above 80 psi is too high; 50–65 psi is normal for most homes.
  • Can I clean a stuck PRV instead of replacing it?
    Minor debris can sometimes be cleared, but many stuck PRVs are worn and should be replaced rather than repeatedly serviced.
  • Will a waterlogged expansion tank cause the same symptoms?
    Yes — a waterlogged expansion tank can prevent pressure relief during thermal expansion and contribute to spikes, so check it when diagnosing PRV issues.

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