Knocking Noise in Water Pipes? 6 Reasons For That Annoying Banging Sound

A recurring knocking noise in water pipes is not only annoying but can signal a problem.  Don’t assume that the clanging will just go away on its own. This guide explores the potential causes of a knocking noise in water pipes so you can fix the issue for good.

1. Water Hammer

Water hammer happens when the water flow in your pipes stops abruptly; for example, when you turn off a faucet or valve quickly, and the flowing water is suddenly stopped. The resulting noise sounds like a loud bang or hammering in your walls. Over time, water hammer can damage your plumbing system.

The Solution

You may need to install a water hammer arrestor, add air chambers, or install a water pressure regulator in your plumbing system to prevent this issue from occurring. A plumbing professional can advise you on the best course of action.

2. High Water Pressure

High water pressure can cause pipes to shake and rattle, creating a banging or knocking noise. When the water pressure is too high, it can affect the water flow rate within the pipes, causing it to bounce off the sides of the pipe and shake it.

The Solution

Test the incoming water pressure in your home; it should be between 40 PSI and 80 PSI. If it’s higher than that, you’ll need a plumber to adjust or replace the water pressure-reducing valve.

3. Thermal Expansion

Hot water can cause metal plumbing pipes to expand as it flows through them. Then, after the hot water stops flowing, the pipes will contract. This expansion and contraction can cause a knocking noise in your pipes, which continues even after the water flow stops.

The Solution

Adding pipe supports can accommodate the natural expansion and contraction of plumbing pipes and reduce that knocking sound. If the pipes are visible, you can install these supports yourself. However, if they’re behind walls, you’ll need a pro.

4. Loose Pipes

When water flows through pipes that aren’t properly secured, it can cause them to rattle and make a knocking noise. Loose pipes aren’t necessarily a problem, but the resulting noise can be irritating.

The Solution

Secure visible plumbing pipes using plumbing straps or clips. However, pipes hidden behind the walls need help from a professional plumber. Securing these means you need to remove a section of the drywall to access the pipes—turning it into a much larger project.

5. Sediment in Water Heater

Over time, sediment builds up in your water heater and settles at the bottom of the tank. As it heats the water, it creates steam bubbles that can escape through the sediment, causing a knocking sound. 

The Solution

Flushing your water heater can get rid of sediment buildup. Unless you’ve done this before, hiring a pro to flush your water heater is best to prevent damage. In some cases, flushing an old water heater that has never been flushed can damage the appliance. Ask the expert if this is the best course of action. 

6. Trapped Air

Air pockets trapped within a plumbing system can also cause a banging or knocking sound. The only way to solve this is to release the trapped air from the system.

The Solution

Open all the valves and faucets in your home to bleed the system and allow the air pockets to escape. If this doesn’t solve the problem, you might need to consult a plumber to ensure your water pressure is at the correct level.

When to Call a Pro

Some causes of knocking noises in water pipes can be fixed by a homeowner with basic DIY skills. If the knocking is caused by trapped air, or loose pipes, you should be able to handle this yourself. You may not be comfortable with this type of project and, in that case, it is best to leave it to a local plumbing repair professional.

A plumber can determine the cause of the knocking noise and recommend the proper repairs. If the sound is caused by water heater sediment buildup, water hammer, or high water pressure, it’s best to call a pro immediately because these are not DIY-friendly fixes. If your pipes need to be replaced, expect to pay $370 to $2,140 for pipe replacement costs.