High pressure causing pipe hammer

Pipe hammering triggered by excessive pressure

Quick Answer:

If your house suddenly bangs or hammers when a washing machine, dishwasher or other fast-closing valve finishes a cycle, the likely cause is a pressure spike combined with energy in the water lines. Quick steps: confirm the noise lines up with fast-closing fixtures, measure static and peak pressure, correct any high baseline pressure and thermal expansion, then add arrestors at the washer, dishwasher and other fast-closing valves and secure loose pipes.

Why This Happens

Water hammer is a pressure surge caused when flowing water is forced to stop quickly. Higher baseline static pressure and thermal expansion store more energy in moving water, so when a solenoid or quick-closing valve snaps shut the resulting spike is louder and stronger. Fast-closing appliances concentrate that shock at a point in the system, and loose pipes let the pipe move and bang off framing.

Long-term high static pressure can wear components and valves — think of High pressure damaging PRV — and rapid valve shuts can damage solenoids and controls, which is why High pressure ruins solenoid valves if left unaddressed.

Step-by-Step What to Do

1) Confirm the hammer coincides with quick-closing fixtures

  • Listen and note when the banging happens (e.g., immediately after washer/dishwasher cycles, ice maker fill, or certain toilets).
  • Run a single cycle with someone watching the pipes, or shut off the supply to one appliance and see if the noise stops. If the hammer always lines up with those valve closures, you have the expected correlation.

2) Measure peak pressure

  • Attach a basic pressure gauge to an exterior hose bib or washing machine supply to read static pressure (normal is about 40–60 psi).
  • While a gauge reads, trigger a fast-closing fixture to see if pressure spikes. Note that household gauges may miss very fast transients — if you suspect very large spikes, a professional with a pressure transducer can capture peak events.
  • Watch for sustained static pressure over ~80 psi or frequent spikes well above 100 psi — those are signs to act quickly.

3) Fix baseline high pressure (PRV and expansion)

  • If static pressure is too high, adjust or install a pressure reducing valve (PRV) so normal pressure is about 50–60 psi. A correctly set PRV reduces the energy available to create big water hammer spikes.
  • Address thermal expansion: if the water heater and closed system cause extra pressure when water heats, install or recharge an expansion tank sized for your system.
  • If you have a failing PRV or an unfamiliar installation, consider replacement by a qualified plumber — PRVs can be tricky to set and test.

4) Add arrestors at washer, dishwasher, and fast-closing valves

  • Install water hammer arrestors (piston or properly rated bladder type) at the supply valves for the washer, dishwasher and any other fast-closing solenoid valves. Place them as close to the valve as practical.
  • Use arrestors rated for hot water and for the line size; a cheap or incorrectly installed arrestor may not help.
  • Remember arrestors are a supplement to fixing baseline pressure and expansion — they reduce the shock at the valve but do not cure high system pressure.

5) Secure loose pipes and straps

  • Locate the noisy runs and add or replace straps and clamps where pipes pass framing. Use cushioned clips where pipes rub against wood.
  • Secure both horizontal and vertical runs so the pipe cannot swing when a pressure spike hits.

6) Test and recheck

  • Run the appliances and cycles that caused the noise. If banging persists, re-measure pressures and inspect arrestor installation and pipe supports.
  • If secure supports, arrestors and correct PRV/expansion settings don’t stop the problem, call a professional for dynamic pressure testing and diagnosis.

What Not to Do

  • Don’t add arrestors as a substitute for fixing high static/expansion—do both in the right order.
  • Don’t jam soft materials into pipe runs hoping to deaden sound; that can hide movement and create wear points.
  • Don’t remove or bypass a PRV without replacing or correctly adjusting it; suddenly higher inlet pressure can damage home plumbing and appliances.

When to Call a Professional

  • If static pressure is over 80 psi or you suspect very high transient spikes (professionals have the right instruments).
  • If the PRV needs replacement, if the expansion tank is failed or inaccessible, or if you’re not comfortable installing arrestors or re-piping/supporting lines.
  • If bang­ing continues after you’ve followed the steps above — persistent hammering can indicate hidden problems like waterlogged arrestors, failing PRV, or pipe layout issues.

Safety Notes

  • Turn off the water supply and relieve pressure before working on lines. Open a faucet to bleed pressure after shutting off the shutoff valve.
  • Be cautious around hot water and water heaters. Allow lines to cool before handling near the heater.
  • If you are not experienced with plumbing tools, soldering, or gas/water heater connections, hire a licensed plumber to avoid damage or injury.

Common Homeowner Questions

  • What pressure should my house have? — Aim for about 50–60 psi at the main; below 40 can hurt appliance performance, above 80 is considered high.
  • Will arrestors stop all banging? — They often reduce noise at specific valves but work best after correcting high baseline pressure and expansion issues.
  • Can I install arrestors myself? — Many homeowners can install arrestors at accessible appliance supply valves, but call a pro for PRV, expansion tank, or hard-to-reach piping work.

Related Articles

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For the full directory, see High Pressure Causing Fixture Damage.

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