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How to Fix a Water Hammer

mediumHome Repair1-2 hours8 steps

Safety Warnings

  • Shut off the main water supply before beginning work to prevent flooding.
  • Ensure all plumbing connections are tightened securely to avoid leaks under pressure.
  • Use caution when working around electrical components or water heaters.

Tools Needed

Adjustable Wrench — 1/2-inch
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Pipe Cutter — Standard copper tubing size
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Materials

Water Hammer Arrestor — Standard threaded(1-2 units)
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Plumber's Tape — Teflon/PTFE(1 roll)
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Steps

1
Identify the location of the knocking sound (the water hammer) and locate the nearest shut-off valve.
Tip: Hammering often occurs near fast-closing valves like those in washing machines or dishwashers.
2
Shut off the main water supply to the affected line to ensure no water flows during the repair.
Tip: Open a faucet at the lowest point of the house to drain remaining water from the pipes.
3
Cut the section of the pipe where the water hammer arrestor will be installed using a pipe cutter.
Tip: Ensure the cut is clean and square to prevent leaks.
4
Apply plumber's tape to the threaded ends of the water hammer arrestor.
Tip: Wrap the tape clockwise to ensure a watertight seal.
5
Install the water hammer arrestor into the pipeline by tightening the fittings with an adjustable wrench.
Tip: Do not over-tighten, as this can crack the fittings or strip the threads.
6
Reassemble the pipeline and ensure all connections are secure.
Tip: Double-check that the arrestor is positioned vertically if specified by the manufacturer.
7
Slowly turn the main water supply back on and check for leaks around the new installation.
Tip: Keep a towel and bucket nearby to catch any minor drips during the initial pressure test.
8
Test the system by opening and quickly closing the faucet or appliance that was causing the noise.
Tip: The arrestor should now absorb the shock wave, eliminating the knocking sound.

Pro Tips

  • Water hammer is caused by a pressure surge when water is stopped abruptly; arrestors act as cushions to absorb this energy.

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Sources

Synthesized from 6 verified sources:

Wikipedia (CC BY-SA 4.0)View →
USDA Farmers' Bulletin (Gutenberg)View →
Wikipedia (CC BY-SA 4.0)View →
Gutenberg: Dwelling ConstructionView →
Gutenberg: Simple Plumbing Repairs (FB 1460)View →
Wikipedia (CC BY-SA 4.0)View →