Quick Answer:
If you hear a hammering or knocking after installing a smart shutoff valve, it’s usually caused by rapid valve closure or pressure/flow changes in the line. First run the valve’s built-in test or auto-close function, compare the sound to a normal fixture shutoff, and make small adjustments to the close-speed setting in the app. If you’re unsure, have a plumber tune the device while keeping leak protection active.
Why This Happens
Smart shutoff valves move to stop flow quickly when they detect a leak or during tests. If the valve closes very fast it can create a pressure spike or a sudden change in flow direction, which then shows up as a hammering noise in nearby pipes or fittings. The same principle explains other common noises like Loud bang when washing machine stops—fast flow changes produce pressure waves that travel through the plumbing. Pipes in longer runs or with loose supports are more likely to make noise.
Step-by-Step What to Do
1. Prepare and reduce risk
- Turn off any sensitive appliances or electronics near the water lines you’ll be testing.
- Let household members know you’ll run a test so no one triggers fixtures during the check.
2. Run the valve’s test or auto-close function
- Open your smart shutoff app and locate the device test, diagnostic, or auto-close feature. Many systems include a test that forces the valve to close for a few seconds.
- Run the test and listen carefully for the hammering sound. Note whether it happens during the automated closure.
3. Compare automated closures to normal fixture shutoffs
- Turn off a normal fixture (faucet or toilet) and listen for the same noise. Comparing helps tell if the valve is closing unusually fast or if the system normally makes that sound.
- If the noise only appears with the valve’s automated closure, the valve speed is the likely cause.
4. Adjust the close-speed setting in small steps
- Find the close- or shutoff-speed setting in the app. Make a small change—don’t jump from fastest to slowest at once.
- Adjust one step, save the setting, then repeat the test. Small increments help you find a balance between response time and noise.
5. Retest and note improvement
- After each adjustment, run the auto-close test and compare the noise level and any pressure symptoms.
- Keep a short record: setting used, whether noise reduced, and whether fixtures behaved normally.
What Not to Do
- Don’t permanently disable leak protection to stop the noise. That defeats the device’s safety purpose.
- Don’t bypass the smart valve with temporary fittings or open a tee to avoid the valve. Temporary bypasses can leak or fail unexpectedly.
- If you can’t confidently adjust close-speed settings, have a plumber configure it while keeping protection active.
When to Call a Professional
Call a plumber if the hammering continues after conservative app adjustments, if you see pressure-related damage (dripping joints, loose fittings), or if you don’t feel confident changing settings. A plumber can fine-tune the valve’s closing profile, add or check water hammer arrestors, and secure loose pipe supports without disabling leak protection.
Safety Notes
- Always keep leak detection and shutoff enabled unless a qualified pro tells you otherwise for a short, supervised task.
- Make small app changes and retest—large sudden changes can mask the problem or create new issues.
- If you smell gas, see electrical sparks, or find major leaks during testing, stop immediately and call the appropriate emergency service and a plumber.
Common Homeowner Questions
- Will slowing the valve damage it? No—manufacturers expect adjustable speeds; use the app’s settings and avoid extremes.
- Could the hammering mean a leak is happening? Not usually; it’s more often a pressure wave. But check for new drips or wet spots to be safe.
- What if the sound is in other parts of the house? That can indicate loose pipes or long runs—consider having a plumber add supports or an arrestor, similar to fixes for Pipes bang when multiple fixtures shut off.
For more related articles, see the Pipes Banging After Fixtures Turn Off hub.