Quick Answer:
If the pressure-reducing valve (PRV) in your house makes a low-frequency vibration only while water is flowing, the valve internals are likely vibrating or cavitating under flow. Verify the vibration by feeling the valve body, make sure upstream and downstream valves are fully open, test the noise at low and high flow, and replace the PRV if the noise continues under normal flow conditions.
Why This Happens
A PRV controls pressure by dropping pressure across an internal seat. When flow is high or the pressure drop is sudden, the flow can become unstable and form tiny vapor bubbles that collapse (cavitation) or force the seat or disc to vibrate. That vibration shows up as a low-frequency hum or buzzing only during flow and can quickly wear the valve and nearby fittings.
Other causes include worn internal parts, debris lodged near the seat, or downstream conditions that change the valve’s operating point. If your pressure seems to swing during the day, check the related note on Pressure fluctuates randomly throughout day for other causes that can make the PRV work harder.
Step-by-Step What to Do
1. Verify the noise is coming from the PRV
- With water flowing, carefully place the flat of your hand on the PRV body to feel for vibration. Keep fingers away from hot pipes and rotating equipment. A vibrating valve body usually confirms the PRV is the source.
2. Confirm upstream and downstream valves are fully open
- Locate the inlet and outlet shut-offs around the PRV and ensure each is turned fully open. Partially closed valves change flow patterns and can cause vibration that sounds like a failing valve.
3. Test noise at low flow vs high flow
- Open a single faucet slowly and listen. Then increase flow to a full tap or run multiple outlets. Note whether the vibration appears only at high flow, only at low flow, or across the range. Persistent vibration at normal household flow is the key concern.
4. Try simple, safe remedies and observe
- If debris is suspected and you are comfortable, isolate and flush the line per the valve manufacturer’s instructions. If you don’t have the instructions, skip this and call a pro.
- Sometimes reducing peak demand (staggering heavy-use appliances) temporarily reduces the noise until a replacement is scheduled.
5. Replace the PRV if buzzing persists under normal flow
- If vibration continues at normal household flow, the PRV is likely failing and should be replaced. A worn seat or spring can cause ongoing cavitation and damage. Replacing the PRV resolves the source and prevents the vibration from loosening joints or causing leaks.
- If the problem happens only when you run many fixtures at once, see the related note on PRV failing only under high demand for high-demand troubleshooting before replacing equipment.
What Not to Do
- Don’t assume it’s harmless noise—vibration can accelerate failure and loosen joints.
- Don’t hammer on the valve, overtighten fittings, or use makeshift braces; that can damage the valve or piping.
- Don’t attempt internal repairs unless you have the correct replacement parts and know how to depressurize the line safely.
When to Call a Professional
- If you can’t confidently identify the PRV as the noise source, call a plumber to diagnose it safely.
- If the vibration continues after the basic checks, arrange a professional replacement—valve removal and installation requires isolating and depressurizing the line and may need adjusting to local code.
- If you see leaks, loose fittings, or pressure drops when the noise appears, call a professional promptly to avoid water damage.
Safety Notes
- Always shut off water to the section you work on and relieve pressure before attempting any repair or removal.
- Wear gloves and eye protection when working on plumbing. Water in the valve may be hot—check temperature before touching.
- If you’re unsure about shutting down the right valves or re-pressurizing the system, stop and call a licensed plumber.
Common Homeowner Questions
- Is the vibration dangerous?
Short answer: It can be—vibration accelerates wear and can loosen joints, so don’t ignore it. - Can I silence it temporarily?
Short answer: Reducing flow demand or isolating the circuit temporarily can stop the noise, but it won’t fix the failing valve long-term. - Will adjusting the PRV setting stop the noise?
Short answer: Not usually; internal wear or cavitation is the common cause and typically requires replacement rather than adjustment.