How to Fix Water Hammer (Banging Pipes)

If your pipes bang, thud, or shudder every time a faucet shuts off or the washing machine fills, you are dealing with water hammer. Learning how to fix water hammer starts with understanding that the noise is not just annoying: it is a pressure shock wave traveling through your plumbing. When flowing water stops suddenly, its momentum has nowhere to go, so it slams into a closed valve and sends a shock back through the pipe. Fix the shock, and the banging stops.

What Water Hammer Actually Is

Water is heavy, and moving water carries a lot of energy. In a typical home, water flows through supply pipes at several feet per second. When a valve closes quickly, that moving column of water stops in a fraction of a second. The kinetic energy converts into a pressure spike that can briefly reach several times your normal water pressure. That spike races back and forth through the pipe, which is why you hear a bang, a series of thuds, or a shudder that seems to travel through the walls.

Some fixtures are far more likely to cause water hammer than others. Washing machines and dishwashers use solenoid valves that snap shut almost instantly. Single-lever faucets, ice makers, and sprinkler valves can do the same. Toilets, by contrast, usually close more gradually and are less common culprits, though a faulty fill valve can still contribute. If the bang happens at the same moment a specific appliance stops filling, you have found your trigger.

Older homes often relied on vertical sections of pipe called air chambers. These trapped a pocket of air near fixtures, and the air acted as a cushion that absorbed the shock. Over time, however, that air dissolves into the water, the chamber fills with water, and the cushion disappears. That process is called waterlogging, and it is one of the most common reasons water hammer appears in a home that used to be quiet.

Why Banging Pipes Should Not Be Ignored

It is tempting to live with the noise, especially if it only happens once in a while. That is a mistake. Repeated pressure spikes stress every weak point in the system. Joints can loosen and start to leak, soldered connections can fatigue, and appliance hoses and valves wear out faster. In severe cases, the shock can crack a fitting or damage a water heater, dishwasher valve, or washing machine inlet valve.

Water hammer can also loosen pipe straps and supports. Once a pipe is free to move, each shock makes it swing and strike framing or drywall, which makes the noise louder and the damage worse. A pipe that bangs hard enough to be heard through a wall is moving with real force. Fixing it early is almost always cheaper than repairing a leak inside a wall later.

There is also a safety angle. Very high pressure combined with repeated shocks increases the risk of a burst supply hose, especially on washing machines. If your home pressure is above 80 psi, the fix is not just about noise: it is about protecting the whole system. A simple pressure test, described below, tells you whether pressure is part of the problem.

Find the Cause Before You Fix Anything

Start by identifying the trigger. Stand near the plumbing while someone runs each suspect fixture and shuts it off. Note exactly which fixture causes the bang and whether the noise comes from one location or seems to travel. A bang near a washing machine points to that valve. A bang throughout the house points to high pressure or a system-wide issue.

Next, test your water pressure with a gauge that screws onto an outdoor hose bib. These gauges cost about 10 to 15 dollars at a hardware store. Normal residential pressure is 40 to 80 psi, and most plumbers aim for 50 to 60 psi. If your reading is above 80 psi, high pressure is very likely contributing, even if a fast valve is the immediate trigger. For more on pressure problems, see our guide to low water pressure causes and fixes, which also explains how pressure regulators work.

Check for loose pipes while you are investigating. Look in basements, crawl spaces, and utility rooms for pipes that move when a fixture shuts off. Missing or broken straps are easy to spot. Also check that main shutoff valves and fixture supply valves are fully open. A partially closed valve can worsen turbulence and noise, though it rarely causes water hammer on its own.

Quick Fixes You Can Try First

Before buying parts, try the simplest steps. First, make sure all valves are fully open, including the main shutoff and the shutoffs at the triggering fixture. Next, secure any loose pipe you can reach with pipe straps or cushioned clamps. Do not over-tighten straps on copper or plastic pipe; the pipe should be held firmly but not crushed, and a small amount of cushioning prevents new rattling.

If the culprit is a washing machine, check its supply hoses. Old rubber hoses should be replaced with braided stainless steel hoses, which handle pressure spikes better. Some homeowners also slow the valve closure slightly by partially closing the washing machine supply valves, but this is only a temporary workaround: it reduces flow and does not fix the underlying shock. Use it to buy time, not as a permanent solution.

For a single noisy faucet, an aerator or cartridge problem is unlikely to be the cause, but a worn cartridge can make a faucet close unevenly. If the faucet drips, sticks, or is hard to operate, replacing the cartridge is worthwhile anyway. In most cases, though, the real fix is an arrestor or a pressure correction, covered next.

Install Water Hammer Arrestors

A water hammer arrestor is a small sealed device containing a piston and a cushion of air or gas. When a pressure spike hits, the piston compresses and absorbs the shock instead of letting it slam through the pipe. Modern arrestors are far more reliable than old air chambers because the air cannot dissolve into the water. They are the standard fix for appliance-triggered water hammer.

Arrestors come in two main styles. Screw-on arrestors attach directly to a washing machine outlet box or a fixture supply valve and require no pipe cutting, making them a good do-it-yourself option. In-line arrestors are soldered or pressed into the supply line near the fixture and are typically installed by a plumber during a repair or remodel. For a washing machine, install one arrestor on the hot line and one on the cold line, as close to the machine valves as possible.

Size matters. Arrestors are rated by fixture units, and a washing machine generally needs a larger unit than a single faucet. Follow the manufacturer sizing chart rather than guessing. A too-small arrestor will quiet the noise only slightly. After installation, test by running the fixture several times and shutting it off abruptly. The bang should be gone or reduced to a faint tap.

Drain and Recharge Air Chambers

If your older home has air chambers and no arrestors, draining the system can restore the air cushion temporarily. Start by turning off the main water supply. Then open the highest faucet in the house and the lowest faucet, usually an outdoor hose bib or basement laundry tap, and let the system drain completely. This allows air back into the chambers.

Once the system is empty, close the lowest faucet first, then turn the main water back on slowly. Let the highest faucet run until the water flows steadily, then close it and open the other faucets one at a time to clear air. This process often silences water hammer for weeks or months, but because the air will dissolve again, it is a temporary fix. If the banging returns quickly, install modern arrestors instead of draining repeatedly.

Note that some newer homes have no air chambers at all, in which case draining will not help. If you are unsure whether your home has them, look for short vertical pipe stubs near fixture shutoffs in a basement or crawl space. When in doubt, an arrestor is the more reliable investment.

Fix High Water Pressure at the Source

If your pressure test reads above 80 psi, you likely have a failed or missing pressure reducing valve, also called a PRV. The PRV sits on the main supply line where water enters the home and reduces municipal pressure to a safe level. When it fails, full street pressure reaches your fixtures, which makes water hammer worse and shortens the life of appliances and valves.

Our guide to water pressure regulator cost breaks down PRV pricing in more detail. If your home has no PRV and municipal pressure is high, installing one is one of the best investments you can make in your plumbing. Set it to 50 to 60 psi and retest after installation.

When to Call a Plumber

Call a plumber if the banging continues after you have installed arrestors and corrected pressure, if you see any leak or water stain near the noisy pipe, or if the noise started suddenly after plumbing work. Sudden onset can signal a broken strap, a dislodged pipe, or a failed valve that needs professional diagnosis. Also call a pro if the PRV needs replacement, if pipes are buried in walls or concrete, or if you are not comfortable shutting off and draining the system.

Water hammer is usually a straightforward fix once the trigger is identified. Test your pressure, secure loose pipes, and add an arrestor at the offending fixture. Correct high pressure at the PRV, and do not keep draining air chambers as a permanent strategy. With the right fix, your pipes should run quietly, and your joints, valves, and appliances will last longer. If you would rather have a professional diagnose the cause, call (877) 762-1902 for help.