Water Hammer Fix
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How to prevent and eliminate water hammer in home water heating systems? What causes the problem, what are the symptoms and how to fix it? What is the water hammer arrestor, how does it work, and how to install one?

What is a water hammer?

It is not uncommon for water heating and plumbing systems to generate loud noise such as banging and thumping, especially when water stops or changes directions suddenly. This problem is known as water hammer, a phenomenon related to the hydraulic shock waves, which can cause a vibration of plumbing pipes when they strike against each other or wooden beams.

What can cause water hammer?

The problem can be found in new and old houses and no matter of the plumbing type of; copper, CPVC, or steel. Depending on the pipe type, the noise level varies. 

Valves. What can cause water hammer to occur is a single-lever faucet and a faucet with the solenoid valve, washing machines, and dishwashers since they are equipped with automatic valves that close fast.

Pressure. The problem can also occur when the water pressure from the main supply pipe is too high. A normal pressure is from 30 to 60 PSI, and to avoid damages to the heater’s elements due to extreme pressure, it is recommended to install a pressure-reducing valve.

Facts about water hammer

  • Water hammer can occur with or without noise.
  • Water hammer can occur to homes with metal and plastic pipes.
  • The noise is greater with the harder pipe material.
  • To prevent damages, the shock waves have to be eliminated.
  • The shock wave can go over 3000 kPa.
  • Water hammer can damage not only pipes but connected appliances.
  • Water hammer suppression devices (such as the air chamber or hammer arrestor) should be installed at each appliance, and a quick closing valve.
  • Water hammer and the shock wave can appear from the house next door.
  • It is recommended to connect the air chamber to a water line in a vertical position.
  • One should be installed on the hot and one on the cold side.
  • Recommended devices to reduce water hammer: air chamber, hammer arrestor, spring-loaded washers, soft closing lever taps, ball valves…

Problems caused by water hammer

  • Loud banging or thumping noise
  • Collapsed flue tube on gas heaters
  • Deformation on the top of the heater
  • Expansion in the tank shell
  • Damages to piping, TPR valve, water meter, pipe joints

How different pipe types respond to water hammer

Metallic pipes

  • Vibration 
  • Excessive noise
  • Damaged valves
  • Noisy valves
  • Loose clips

Plastic pipes

  • Vibration
  • Reduced noise
  • Cracked pipe
  • Damaged valves
  • Noisy valves
  • Loose connections and leak
  • Clips breaking

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Troubleshooting and how to stop water hammer

There are several approaches on how to prevent or eliminate water hammer.

  1. The simplest solution for this problem is to turn the tap off slowly so the water inside the plumbing system can slow down gradually.
  2. Secure the loose pipes. Install or tighten any loose pipe straps that secure the tubing to the wooden frame. You can also put a pipe sleeve insulation onto the pipes. This is possible only there where the pipes are exposed and not hidden behind the walls.
  3. If the above suggestions do not solve the problem, you might have to install a device called an arrestor.
  4. There are some suggestions from the manufacturers, such as Bradford White, that the problem can be solved by installing an expansion tank and pressure relief valves with the setting at 25-50 pounds less than the TPR valve on the heater.

How does the arrestor work?

Water hammer arrestorWater hammer arrestor
(from amazon.com)

A water hammer arrestor, also known as an air cushion or air chamber, is a simple device where inside of its cylindrical body is a pre-charged and sealed air chamber. The chamber is divided by the sliding piston. A side that connects to the plumbing is filled with water, while on the other side of the piston is air. Since the chamber is sealed, there will be no air or water leak.

While the sudden water pressure increases, the sliding piston moves toward the air chamber compressing the air, so the vibrations will dissipate into the cushion of air, protecting the system from high-pressure shocks.

The water comes from the side, which is connected to the plumbing.

The arrestor can also fail. The air chamber can become filled with water reducing its performance. Also, it can get clogged with the accumulated mineral deposits and debris, requiring proper cleaning.

Note: The air is factory charged. Some models are rechargeable, and some are not.

How to install an arrestor?

Required tools

  • Adjustable wrench
  • Pipe wrench
  • Pliers
  • Torch
  • Solder
  • Cutting tools


An arrestor for home use is easy to install. The arrestor should be installed near the water heater, as close as possible to quick-closing valves, and on the same pipe where the hydraulic disturbance appears. The arrestors are available for standard pipe sizes of ½” and ¾” or larger diameter. Due to the smaller size of the device, it can be easily installed inside a wall.

Arrestors can be installed in new and existing homes and plumbing systems, positioned horizontally, vertically, or at any angle. Some models are designed for threaded applications, compression installation, quick T-connect, brass adapter, PEX and copper installation, etc.

Follow the installation tips below:

  • Turn off the water supply.
  • Drain the pipe that makes the noise and where the arrestor will be installed.
  • If you have copper pipes, cut the pipe and prepare for soldering.
  • Connect the pipes to a T-fitting.
  • Screw the arrestor on the threaded T fitting.


A water hammer does not occur only in water heating systems. It can happen when running a washing machine, dishwasher or when flushing a toilet. The arrestors are the most common way of the water hammer repair and should be installed on the pipe where it occurs.