Banging Pipes When Water Shuts Off

What Is Making the Bang?

When you close a valve, the water in the pipe has nowhere to go. It is moving, it has weight, and it stops fast. The shock travels back through the pipe and the pipe knocks against whatever is next to it. That is water hammer.

A dishwasher, a washing machine and a toilet fill valve all shut off quickly, so they are the usual culprits. A single-handle faucet that you snap closed does the same thing.

Not every bang is water hammer, though. Four things cause most of the noise in a home:

• Water hammer from a fast valve. One sharp bang right when water stops.
• Loose pipes. The pipe is not hammering, it is moving and hitting a joist, a strap or another pipe. You hear knocking, ticking or rattling, often when water starts as well as when it stops.
• High water pressure. Strong pressure makes every shut-off harder. If the bangs show up with spraying faucets, read water pressure too high.
• Missing or worn air chambers. Many homes have a short capped pipe, or a small shock absorber, near fixtures to cushion the stop. When it fills with water, it stops cushioning.

Which One Do You Have? Three Quick Tests

You do not need tools for these. Just a few minutes and someone to help listen.

1. Find the fixture. Run each faucet, then close it fast. If one faucet or appliance always sets off the bang, the problem is near that fixture. If every fixture does it, look at the whole house.
2. Close it slowly. Shut a faucet slowly instead of snapping it. If the bang goes away, a fast valve is the trigger and the fix is a cushion for the pipe, not a new pipe.
3. Listen when water starts. A bang on shut-off only points to water hammer. Knocking or ticking when water starts or when hot water runs points to a loose or expanding pipe.

Pay attention to where the sound seems to come from. A crawlspace, a basement ceiling or an open stud wall lets you look at the pipes. If you can see a pipe jumping against a joist, you have found it.

Houses on a Well Hear This More Often

A lot of homes in the North Georgia mountains run on a well. A well has a pressure switch and a pressure tank. That tank is a cushion for the whole system. When the tank has lost its air charge, the system loses its shock absorber and the pump can cycle hard.

If your bangs come with a pump that kicks on and off every few seconds, or pressure that jumps from strong to weak, the problem may be the tank and not the pipes. Read well pump short cycling for that pattern. Ryan installs well bladder tanks and well pumps.

On a well, do not guess at pressure settings. The switch and the tank are set to work together. Changing one without the other makes things worse.

What Is Safe to Try Yourself

• Close faucets and valves slowly. It costs nothing and helps right away.
• Look for pipes touching wood, metal or each other in a basement or crawlspace. Gently pad or separate any pipe you can reach, but do not bend copper.
• Check whether the noise follows one appliance. If it is the washing machine, look at the hoses and valves behind it.
• Drain the pipes to refill any air cushion: shut off the main water valve, open the highest and the lowest faucets until the water stops, then close them and turn the main back on slowly. If you are not sure where your main valve is, see how to shut off your water main.

If that does not stop it, the next step is a fix that goes on the pipe: a hammer arrester at the fixture, new straps, or a pressure check. Those are quick jobs for a plumber, and cheaper than the damage from pipes that keep slamming for years.

When a Bang Is More Than Noise

A bang on its own is a nuisance. A bang plus any of these is a reason to act the same day:

• A drip, a wet spot or a stain near the wall where the noise comes from.
• A pipe that moves visibly when water stops.
• Pressure that changed suddenly, high or low.
• Noise during freezing weather. Pipes that are frozen or thawing can act strangely. See frozen pipes, and if a pipe has split, burst pipe.

Repeated hammering loosens joints over time. Slow leaks inside a wall often start at a joint that has been hit thousands of times. If you find water, leak repair is the next step, and the guide to finding a hidden leak will help you track it.

What Ryan Does About It

Ryan Chastain is a licensed Master Plumber, Georgia license MPR108473. He listens first, finds which fixture or pipe is the trigger, checks your pressure, and tells you what will stop it. The estimate is free. There is no trip fee and no diagnostic fee, so you know the price before any work starts.

Work is backed by a warranty, and the terms are given to you in writing at the estimate. He answers his own phone. Text works best in the mountains, because a text can get through when a call will not. A short video of the noise, with the sound on, helps a lot.