Quick Answer:
A failing pressure reducing valve (PRV) can cause sudden pressure surges that make pipes bang even when no water is being used. Keep a simple log of each event and where you hear it, check if neighbors hear it at the same times, and listen near the water heater and the main service entry to localize the source. If the pattern points to a supply-side problem, have a licensed plumber confirm and fix the pressure-control components safely.
Why This Happens
A PRV keeps city water pressure at a steady level for your home. When it fails or partially sticks, it can open and close rapidly or allow short pressure spikes. Those rapid changes create hammer-like forces in pipes. Similar sounds can come from the water heater, a waterlogged expansion tank, or from sudden changes on the municipal supply.
Step-by-Step What to Do
1. Note the time of each bang
- Keep a short written or phone log with the exact time and a one-word note about how long it lasted (short/long).
- Patterns—same times each day or random—help a professional narrow the cause.
2. Check if it aligns with neighbors or city pressure changes
- Ask a near neighbor if they hear the same noise at the same times. If they do, the issue may be on the supply side.
- Check any municipal outage or work notices you might receive; main valves or pumping changes can create pressure swings.
3. Listen near the water heater and main service entry
- Walk the house and listen closely at the water heater and at the point where the main water line enters your home. Localizing the sound narrows the likely component — heater, PRV, or incoming supply.
- If it sounds strongest at the heater, mention that to the plumber; if at the main entry, that points more to a supply or PRV issue.
4. Isolate briefly and observe
- If you know where your house main shutoff is and can operate it safely, briefly close it to see whether the banging stops. If it stops, the cause is likely on the supply side. If it continues, the problem is internal (heater, expansion tank, or internal valves).
- Avoid prolonged isolation or repeated cycling of valves; this is just a diagnostic check.
5. Record what you find and keep fixtures off while monitoring
- Turn off or avoid using fixtures when you’re monitoring so the bangs aren’t caused by intermittent appliance use.
- If you have automated devices, note whether they run at the same times. For guidance on interactions with automation, see Banging with smart shutoff installed.
- If you find no obvious source inside the house, but the noise continues, it may be unexplained supply-side activity — note those details for the plumber or utility. For general troubleshooting when there is no visible cause, see Banging with no apparent cause.
What Not to Do
- Don’t start opening walls or disabling safety devices; if bangs continue with no fixtures running, have a plumber evaluate pressure control components.
- Don’t attempt to repair or adjust the PRV, water heater relief valve, or expansion tank unless you are a licensed professional.
- Don’t ignore persistent banging — repeated pressure surges stress joints and fittings and can lead to leaks or pipe damage over time.
When to Call a Professional
- Call a licensed plumber if the bangs are frequent, loud, or continue after basic checks.
- Also call if you see leaking, a constantly dripping pressure relief valve on the water heater, a sudden rise in household pressure, or if you’re uncomfortable operating the main shutoff.
- A plumber can safely measure supply pressure, test the PRV and expansion tank, and confirm whether the issue is on the municipal side so the utility can be contacted if needed.
Safety Notes
- Do not tamper with the water heater’s temperature-pressure relief valve or try to disassemble the PRV.
- When operating the main shutoff, know how to reopen it and be prepared for a temporary loss of water. If you’re unsure where it is, wait for a plumber.
- If you smell gas or suspect electrical issues while investigating, leave the area and call the appropriate emergency service.
Common Homeowner Questions
- Is this an emergency? — Not always; intermittent bangs can wait for a same-day appointment, but if you hear loud, continuous banging or see leaks, call now.
- Will replacing the PRV fix it? — Often yes if the PRV is the source, but a plumber will test pressure and check related parts first.
- Can the city cause this? — Yes; sudden pump activity or pressure adjustments in the municipal system can cause supply-side surges.
For more related articles, see the Random Banging With No Water Running hub.