Quick Answer:
Very low or no flow downstream while upstream pressure exists — the pressure reducing valve (PRV) is likely stuck closed. First confirm the upstream supply is present. Then compare gauge readings upstream versus downstream of the PRV; if upstream pressure looks normal and downstream is near zero, the PRV is stuck closed and should be replaced.
Why This Happens
A PRV can seize closed from corrosion, debris, internal spring failure, or valve seat problems. When the valve can’t open it blocks flow to the downstream plumbing while the supply side still shows normal pressure. That trapped condition can leave fixtures dry even though the main or meter shows water available.
Step-by-Step What to Do
Step 1 — Confirm upstream supply is present
- Check the main meter or the municipal shutoff to make sure water is being delivered to the property.
- Try an upstream outlet (before the PRV) if available, or look at a pressure gauge on the supply side to verify normal pressure.
Step 2 — Shut off and limit downstream use
- Turn off major downstream fixtures to avoid damage if the valve suddenly frees. Do not keep running taps or appliances.
Step 3 — Compare pressure gauges upstream vs downstream of the PRV
- Read the pressure upstream of the PRV and then immediately downstream. Use properly rated gauges or a qualified technician’s gauges.
- Interpretation: if upstream shows a normal pressure (for example, 40–80 psi depending on your system) and downstream is at or very near zero, the PRV is stuck closed.
Step 4 — Decide on replacement
- If the checks above show upstream pressure present and downstream near zero, the PRV should be replaced rather than repeatedly worked on.
- For specifics on diagnostic testing before replacement, see How to test PRV failure.
- Replacement typically requires isolating the line, draining downstream, and installing a new PRV sized and rated for your system — this is commonly done by a plumber.
What Not to Do
- Don’t keep forcing usage of downstream fixtures; continuing to run water against a stuck valve can cause damage when the valve suddenly gives.
- Don’t try to force the valve open with excessive tools or impact. A stuck-closed PRV can fail suddenly when freed and create a high‑pressure surge or leak.
- Don’t bypass the valve with makeshift plumbing or tape. Temporary bypasses can create unsafe pressures and violate local codes.
When to Call a Professional
- If you don’t have gauges or can’t safely isolate the line, call a licensed plumber.
- Call a pro if the valve is leaking, the inlet or outlet connections are corroded, or if you suspect more complex system damage.
- Contact a professional if you need the PRV replaced and you’re unsure about sizing, backflow requirements, or local code compliance.
Safety Notes
- Always shut off the main water supply and relieve downstream pressure before removing or replacing a PRV.
- Wear safety glasses and protect nearby electrical devices from water when working on plumbing.
- If the system has a booster pump, water heater, or backflow device, be aware those components can be affected; isolate and follow manufacturer instructions or consult a pro.
- When in doubt, stop and call a licensed plumber rather than attempting risky repairs.
Common Homeowner Questions
- What causes a PRV to stick closed? — Corrosion, debris buildup, a broken internal spring, or mechanical wear can prevent the valve from opening.
- Can I temporarily bypass a stuck PRV? — It’s not recommended; bypassing can create unsafe pressures and may damage plumbing or violate codes.
- Will a stuck-closed PRV damage my plumbing? — It can cause appliances or fixtures to run dry and may create pressure changes when it fails; replacement is the safe fix.