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Fix pipes that hammer

We'll install water hammer arrestors and tighten loose pipe straps—or tell you when to call a pro.

Troubleshooting · Home plumbing
30–60 min
What you'll need
  • Water hammer arrestors (match the size of your supply lines)
  • Adjustable wrench or channel locks
  • Pipe straps and screws (if adding or replacing)
  • Foam pipe insulation or rubber pads (optional)
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Steps

Goal: Confirm the symptom, install arrestors, tighten straps—or call a pro if the noise persists.

  • Listen for a bang or knock when you turn off a faucet, flush a toilet, or when a washing machine or dishwasher cycle ends.
  • Good: Bang or knock at a specific fixture—water hammer. Proceed to Install water hammer arrestors.
  • Bad: Different noise (hum, rattle)—may be a different problem. See When to get help.

Install water hammer arrestors

Goal: Absorb the pressure wave when flow stops.

  • Identify the fixture or appliance that causes the hammer—usually a washing machine, dishwasher, or quick-closing faucet.
  • Shut off the water supply to that fixture. Drain the line by opening the faucet or disconnecting the supply.
  • Install a water hammer arrestor on each supply line (hot and cold) as close to the fixture as possible. Screw the arrestor onto the shutoff valve, then reconnect the supply line to the arrestor.
  • Turn the water back on and test. Check that shutoff valves are fully open.
  • Good: Hammer reduced or gone. Problem fixed.
  • Bad: Still hammering—proceed to Tighten pipe straps.

Tighten pipe straps

Goal: Secure loose pipes that amplify the shock.

  • Inspect pipes in the basement, crawl space, or under sinks. Look for pipe straps that are loose or missing.
  • Tighten screws on existing straps and add straps where pipes are unsupported. Add foam or rubber cushioning where pipes contact framing.
  • Good: Straps snug, pipes stable. Hammer reduced or gone.
  • Bad: Still hammering—call a plumber. High water pressure or system-wide issues may need a pro.

When to get help

Call a plumber if:

  • The hammer persists after installing arrestors and tightening straps.
  • You hear hammer throughout the house.
  • You are not comfortable working with supply lines.

Verification

  • No bang or knock when you turn off the faucet or appliance that caused the hammer.
  • Pipes are stable and straps are snug.
  • Shutoff valves are fully open.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Confirm symptom Verify the bang or knock happens when flow stops; identify the culprit fixture.
  2. Install arrestors Install water hammer arrestors at the supply lines to the culprit fixture.
  3. Tighten straps Tighten loose pipe straps and add cushioning at contact points.
  4. Call a pro Noise persists, hammer throughout house, or high pressure—call a plumber.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Which fixture or appliance causes the hammer
  • Whether arrestors are installed
  • Whether straps are tightened
  • Steps already tried

Do you hear a bang or knock when you turn off a faucet or appliance?

Water hammer happens at the moment flow stops. Identify which fixture or appliance causes it.

Listen when you turn off faucets, flush toilets, or when the washing machine or dishwasher cycle ends. Good: bang or knock at a specific fixture—water hammer. Bad: different noise (hum, rattle)—may be a different problem.

Yes No

You can change your answer later.

Which fixture or appliance causes the hammer?

The culprit is usually a quick-closing valve or solenoid—washing machine, dishwasher, or a specific faucet.

Turn off faucets one at a time, run and stop the washing machine or dishwasher. Note which action triggers the hammer. Good: you know the culprit. Bad: cannot identify—try arrestors at the main fixtures.

Yes No

You can change your answer later.

Install water hammer arrestors

Install arrestors on the supply lines to the culprit fixture. Shut off water, drain, install, reconnect.

Shut off water to the fixture. Drain the line. Install a water hammer arrestor on each supply line (hot and cold) as close to the fixture as possible. Reconnect and turn water back on. Good: hammer reduced or gone. Bad: still hammering—tighten straps.

Yes No

You can change your answer later.

Tighten loose pipe straps

Loose straps allow pipes to move and amplify the shock. Tighten and add cushioning.

Inspect pipes for loose pipe straps. Tighten screws and add straps where needed. Add foam or rubber cushioning where pipes contact framing. Good: hammer reduced or gone. Bad: still hammering—call a pro.

Yes No

You can change your answer later.

Hammer fixed

The bang or knock is gone or greatly reduced. No further action needed unless the noise returns.

Done

Call a plumber

If the hammer persists after installing arrestors and tightening straps, or if you hear hammer throughout the house, call a plumber. High water pressure or system-wide issues may need a pro.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

What causes water hammer?
Water hammer occurs when water flow stops suddenly—a valve closes quickly, or a washing machine or dishwasher solenoid shuts off. The momentum of the water creates a pressure wave that bangs against the pipes. Loose pipe straps amplify the noise.
Can I fix water hammer myself?
Yes. Install water hammer arrestors at the supply lines to the fixture or appliance that causes the noise. Tighten loose pipe straps and add cushioning where pipes contact framing. Both steps are DIY-friendly.
When should I call a plumber for water hammer?
Call a plumber if the noise persists after installing arrestors and tightening straps, if you hear hammer throughout the house, or if you are not comfortable working with supply lines. A pro can also check for high water pressure.

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