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True Trade Path

Diagnostic guide

Water Hammer

Loud banging in your pipes when you shut off a faucet or valve — what causes it and how to stop it before it damages fittings.

System
Plumbing
Causes covered
6
You can check
5 without a technician

Stop and read this first

  • Repeated water hammer can split pipe fittings and cause leaks inside walls — address it before damage occurs.
  • Do not reduce pressure below 40 psi — fixtures and appliances need adequate flow.
  • If banging started suddenly after a plumbing repair, the new valve may be the wrong type for the application.

Work through these in order

Ordered from most to least likely. Working top down means you rule out the cheap, common causes before paying anyone to look at the expensive, rare ones.

  1. No air chamber or water hammer arrestor installed

    CommonYou can check
    How to check
    Banging occurs when a fast-closing valve shuts — washing machine, dishwasher, or a quick-closing faucet.
    The fix
    Install water hammer arrestors on the supply lines to fast-closing appliances ($15 to $40 each DIY, $100 to $200 per appliance professionally).

  2. Waterlogged air chamber

    CommonYou can check
    How to check
    Home has vertical pipes capped at the top near fixtures (old-style air chambers). Banging returned gradually over time.
    The fix
    Shut off the main valve, open the highest faucet in the house, and drain the system. Close the faucet and turn water back on slowly to recharge the air chambers.

  3. Loose pipe straps or hangers

    CommonYou can check
    How to check
    Banging is accompanied by rattling. Pipes in walls or basement are not secured every 6 to 8 feet.
    The fix
    Add pipe straps or cushion loose pipes with foam insulation. Do not over-tighten — pipes need slight movement.

  4. High water pressure

    CommonNeeds a pro
    How to check
    Pressure exceeds 80 psi at a test gauge on a hose bib. Banging is worse at multiple fixtures.
    The fix
    Adjust or replace the pressure regulator ($250 to $500). Ideal residential pressure is 50 to 60 psi.

  5. Fast-closing solenoid valves in appliances

    CommonYou can check
    How to check
    Banging occurs specifically when the washing machine or dishwasher cycles.
    The fix
    Install arrestors on the appliance supply lines. Most new washing machine hoses include built-in arrestors.

  6. Worn faucet cartridge or valve seat

    PossibleYou can check
    How to check
    Banging at one fixture only. Faucet is old or drips after shutting off.
    The fix
    Replace the faucet cartridge ($15 to $50 DIY) or the faucet ($150 to $400 installed).

Once you know what it is

Step one

Know what it should cost

Get the range before you call, so the first number you hear is not the only number you have.

Step two

Decide repair or replace

On equipment near end of life, the repair is usually the first of several.

Step three

Check the quote

Compare against the typical range and confirm the terms before you sign.

Whole-House Repiping cost guideRepair or replace calculatorEstimate repair costAnalyze a quote

What the fix costs

Tools for this decision

Other symptoms