Home / Common plumbing problems / Pipes banging
Plumbing problem
Why are my pipes knocking or banging?
The short answer
A bang in the pipes right after a faucet, toilet, or washing machine valve shuts off is usually water hammer: a momentary jump in pressure when moving water is suddenly stopped. The pressure wave travels back and forth through the pipe and “bangs” until it dies out (National Environmental Services Center). Left alone, it can damage pipes, fittings, and valves and cause leaks.
What people usually report
A single loud knock or a series of thuds in the wall when a faucet is shut quickly, when the washing machine or dishwasher stops filling, or when a toilet finishes refilling. Some hear a rattle along a run of pipe; others hear it only at night when the house is quiet.
What official sources say the causes can include
- A valve closing quickly. When a rapidly closed valve stops water flowing in a pipe, the energy goes into the valve and pipe wall and sets up shock waves. The fact sheet notes anyone who has lived in an older house knows the bang when a faucet is suddenly closed (National Environmental Services Center, West Virginia University).
- Trapped air and temperature changes. Air trapped in a line compresses and adds pressure, and temperature changes make water expand or contract (National Environmental Services Center, West Virginia University).
- High pressure or loose pipe. Rheem lists adjusting water pressure and securing loose piping among the fixes for knocking and banging, along with a water hammer arrestor (Rheem).
Why it is worth fixing
Water hammer and surge, a slower swing in pressure, both damage pipes, fittings, and valves if they are not controlled, causing leaks and shortening the life of the system. Neither the pipe nor the water compresses to absorb the shock (National Environmental Services Center, West Virginia University).
How to find out
- Match the bang to a fixture. Run each faucet, flush each toilet, and start the washer one at a time, then shut each off. Note which one triggers it.
- Measure the pressure. A gauge on an outside faucet gives a reading. Bremerton suggests a pressure reducing valve above 80 psi, and Cobb County expects 80 psi or less (City of Bremerton, WA, Public Works; Cobb County Water System, GA). See water pressure for how to read it.
- Check for leaks afterward. Look under sinks and at visible joints near the pipes that bang.
If the bang comes from the water heater rather than the pipes, see water heater noises.
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Local help
Who to contact
If you are on a public water system, your water utility is the first call for anything that affects the water itself. Its phone number is on your bill and in its annual water quality report.
For work on the pipes and fixtures inside your home, hire a licensed plumber and confirm the license before work starts. Our guide to choosing a plumber covers what to ask. License lookups for the areas our city pages cover:
- FL: Florida Department of Business and Professional Regulation (DBPR)
- IA: Iowa Plumbing and Mechanical Systems Board (PMSB), administered by Iowa DIAL
- MO: Kansas City, MO City Planning & Development (plumbing license, city-issued)
- NE: City of Omaha Building and Development Division (plumbing license, city-issued; Nebraska has no statewide plumbing board)
- NV: Nevada State Contractors Board (NSCB), Classification C (plumbing)
- OK: Oklahoma Construction Industries Board (CIB)
- TX: Texas State Board of Plumbing Examiners (TSBPE)
Elsewhere, search your state’s plumbing or contractor licensing board. Some cities issue plumbing licenses themselves.
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Common questions
Banging pipe questions
How do I stop my water pipes from banging?
Rheem, a water heater manufacturer, lists three fixes for knocking and banging caused by water hammer: install a water hammer arrestor, adjust the water pressure, and secure loose piping. Measuring your pressure first tells you whether the second one applies; several utilities expect household pressure at or below 80 psi.
Why are my pipes banging even though no water is running?
The National Environmental Services Center fact sheet notes that temperature changes make water expand or contract and affect pressure in the lines. Rheem describes ticking from pipe expansion as temperatures change as normal. Banging with no water in use and no heating cycle is worth describing to a plumber, along with when it happens.
When should I be concerned about water hammer?
The National Environmental Services Center says that if water hammer is not controlled, it damages pipes and valves, causing leaks and shortening the life of the system. A bang that is new, getting louder, or followed by a leak or a drop in pressure is a reason to have it checked.
Sources and limits
- National Environmental Services Center, West Virginia University, Water Hammer (National Drinking Water Clearinghouse fact sheet). Checked 2026-10-05.
- Rheem (water heater manufacturer), The Ultimate Guide to Water Heater Noises: What's Normal (and What Isn't). Checked 2026-10-05.
- City of Bremerton, WA, Public Works, Water Pressure. Checked 2026-10-05.
- Cobb County Water System, GA, Home Water Basics: Pipes, Pressure & Protection. Checked 2026-10-05.
This page summarizes guidance published by the agencies and organizations listed above. It is general information, not a diagnosis of your home or your water. Guidance can change, so check the linked source, your water utility, or your local health department before acting on it. PlumbingRepairCost is not affiliated with any agency named here. Spotted an error? Email hello@plumbingrepaircost.com and we will check it against the source.