What is a water hammer sound?

A water hammer sound is a single sharp BANG that occurs right after a valve closes. That sudden stop creates a shockwave in the plumbing line. When water is moving and gets stopped quickly, the momentum has to go somewhere, so the pressure wave hits fittings, valves, and pipe supports.

Why do I hear knocking pipes when water is not running?

Knocking pipes when water is not running is usually caused by ice maker cycles, toilet tank refills slowly after a flush, irrigation valves closing, or a pressure/air issue that makes the system react. These are quick-closing valves that people often forget exist.

Why does my plumbing bang at night when nobody's using water?

The middle of the night banging is usually due to ice maker cycles, toilet tank refills, irrigation valves closing, or a pressure/air issue making the system react. These automatic fixtures can cause water hammer sounds even when no one is actively using water.

How do I stop the water hammer sound in my pipes?

Water hammer arrestors can work if they're installed in the right place, ideally close to the quick-closing valve or appliance causing the shock, usually within six feet. You can also track the trigger by identifying what fixture just ran before the bang, check for loose pipe movement in accessible areas, and determine if it's hot-water related thermal expansion rather than true water hammer.

Will an expansion tank stop water hammer?

While an expansion tank is great for thermal expansion pressure changes, they're not designed to be used as true water-hammer control devices. Water hammer arrestors are the proper solution for stopping water hammer sounds.

What's the difference between water hammer and thermal expansion noise?

One loud bang at shutoff is likely water hammer. Rapid ticking or clicking after hot water use is often thermal expansion caused by a hot pipe rubbing a stud or joist as it grows and cools. Random knocking when no one's using water is usually a hidden quick-close event from an ice maker, toilet, or irrigation system.

Ask the Colonial Plumbers: What Is That Banging Sound Inside My Pipes?

If you’ve ever heard a loud BANG somewhere in your house after you shut a faucet off or you hear your pipes making noise when water is turned off, you might be picturing a pipe bursting inside a wall.

The good news is that most of the time it has nothing to do with a pipe leak. Instead, it’s your plumbing system reacting to a sudden change in flow or temperature. That said, each type of “bang” can mean something different. Our Colonial Plumbing & Heating co., Inc. team will explain this below.

Is it a water hammer sound or something else?

A classic water hammer sound is a single sharp BANG right after a valve closes. That sudden stop creates a shockwave in the line. However, not every “banging pipe” is water hammer.

Here are three quick “sound IDs” we use in the field:

One loud bang at shutoff = likely water hammer.
Rapid ticking or clicking after hot water use = often thermal expansion caused by a hot pipe rubbing a stud or joist as it grows and cools.
Random knocking when no one’s using water = usually a “hidden” quick-close event coming from an ice maker, toilet fill, irrigation or a pressure or air issue.

Knowing the difference between the banging sounds matters because when people search knocking pipes when water is not running or pipes making noise when water is turned off, they’re usually describing either a quick-closing valve they forgot exists, or a system that’s a little out of balance because of pressure, air pockets, or loose supports.

Why do pipes bang when the water turns off?

When water is moving and gets stopped quickly, the momentum has to go somewhere, so the pressure wave hits fittings, valves, and pipe supports.

If the pipes aren’t secured well or the pressure is higher than it should be, the noise gets louder and travels farther.

Why does it bang at night when nobody’s running water?

The “middle of the night” bang can jolt you awake, making you hop out of bed to see if a pipe has broken somewhere in your home. However, the cause usually isn’t that drastic. Instead, knocking pipes when water is not running is usually due to:

Ice maker cycles
Toilet tank refills slowly after a flush
Irrigation valves close
A pressure/air issue makes the system “react”

Is there anything the water hammer sound or pipes making noise when water is turned off?

Yes. There are strategies that can make the knocking pipes when water is not running stop.

Water hammer arrestors can work if they’re installed in the right place. The best practice is to put the arrester close to the quick-closing valve or appliance causing the shock, usually within six feet.

One common misconception is that adding an expansion take will stop the water hammer sound. That’s not exactly true for this particular type of banging sound. While an expansion tank is great for thermal expansion pressure changes, they’re not to be used as true water-hammer control devices.

3 DIY Tips to Stop the Water Hammer Sound at Home

Sometimes you can fix the issue on your own without professional help or at least track down the source of the water hammer sound or why you have knocking pipes when water is not running.

Track the trigger: Ask yourself what fixture or appliance just ran right before the bang
Look for loose pipe movement: If you can access a basement/crawl/utility area, see if a line visibly jumps when a valve closes.
Check whether it’s hot-water related: If the noise is ticking after showers or dishwashing, it’s more likely expansion or rubbing than water hammer sound.

When it’s time to call Colonial

If you’re hearing a water hammer sound, or you’ve got knocking pipes when water is not running that’s waking you up, don’t ignore it. Repeated hammering can stress joints and valves, and “mystery banging” usually means a fixable issue is building momentum into something that could turn into a major repair job if not addressed.

When Colonial shows up in our fully stocked trucks, we isolate the trigger, confirm the issue and make the best fix after consulting with you. If you want it to be handled quickly, call Colonial Plumbing & Heating Co., Inc. at (804) 526-8415.