What Causes Banging Pipes and How to Stop Them

The washing machine stops filling and you hear it. BANG! from inside your wall. What is that noise? And how do you stop it?

There are a few things that can cause noise and bangs to come from your plumbing. While a water hammer is one explanation, starting with survey of all your visible water lines can help you fix or rule out any other causes.

Assessing visible water lines

Check all your visible water lines. Start gently pushing and pulling on any visible pipes to see if they move. If you find any length of pipe over 16” that moves with a light push, mark it with a piece of tape to come back to after you’ve finished looking over everything. To prevent the pipes from touching the surround building materials, water lines should have support every 16” and at every change of direction.

Locate any internal or external holes that water lines pass through to see if when gently pushed, if the water lines touch the sides in any direction. Any water line that passes through a hole should have a support installed or expandable foam applied which can also keep pests and insects from traveling through a hole. On any large holes in wood plates, a combination of a j-hook and foam pipe insulation wrap can cushion them against any wood or drywall.


What is a water hammer?

If you’ve assessed your pipes and fixed any other issues, the sound you heard may be hydraulic shock – more commonly known as a water hammer. Water hammers occur when the flow of water is abruptly stopped, and the pressure resonates through the pipes causing waves inside the pipes and creating a hammer sound. It could sound like a loud bang, a series of bangs or shuddering, and can occur anywhere water shuts off quickly such as at a washing machine, dishwasher or toilet. While annoying, the water hammer has likely not caused damage to your pipes.



How to fix and prevent water hammer

The easiest way to prevent and fix a water hammer is to create a space before the outlet filled with gas or air that can absorb the pressure. In older homes, this was originally sometimes accomplished by creating an air chamber, a piece of capped off vertical pipe near the outlet. Air chambers often end up filled with water from the pressure changes and no longer work to absorb the shock without draining the entire system to “recharge” the air chamber. A more practical and enduring solution is using water hammer arrestors. Water hammer arrestors, like Oatey’s Quiet Pipes, create space for the water to move when there is a shock but feature a piston design in a sealed pressurized chamber to prevent water from remaining in the arrestor. This design also allows for the water hammer arrestors to be installed at any angle and still absorb shock.

Installing water hammer arrestors can be done at any time, although during construction is preferred to prevent water hammers and protect your plumbing systems.

There are a few things that might cause banging pipes. By assessing your plumbing and securing any lose pipes and installing water hammers, most banging pipes can be fixed or prevented.


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