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🍁 Built for Canadian homes — written to Canadian codes and provincial rules. Not intended for use outside Canada.
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Pipes bang or hammer when taps or appliances shut off

That bang is startling, but it's rarely an emergency — it's usually a lost air cushion that a homeowner can often restore for free.

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Select anything that matches and the checklist below reorders to fit. Not sure? Skip it.
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In Canadian homes, suspect lost air cushion first. If the bang shows up on several taps and got worse over the years, the air chambers have likely waterlogged. It costs nothing to test the fix: shut off the main, open the highest and lowest taps to drain the system fully, then close them and turn the water back on — the recharged air often quiets the hammer. Read the safety note before you touch the main.

Ranked from real-world failure data. The order updates as you select what you’re noticing above.

Likely causes, in the order to check them

Showing the typical order
Beginner-friendly Doable, with care Safety-critical Call a pro

visibilityHow to check

  1. Run several different taps and note whether the bang shows up in more than one place — a system-wide hammer that has worsened over years points to waterlogged air chambers rather than a single loose pipe or appliance.
  2. Locate your main water shutoff now, before you need it — usually where the supply enters the basement or a utility room, or at the water meter. You'll need to reach it to recharge the chambers.
  3. If draining and recharging the system quiets the hammer (see the fix), waterlogged chambers are confirmed. If the noise returns quickly, the home may lack air chambers entirely and need an arrestor instead.
buildNo tools schedule10 min

handymanHow to fix it

warning Know where your main shutoff is firstRecharging the air chambers means shutting off the main water supply and draining the whole house through open taps. That's low-risk work, but only if you can actually reach and close the main — locate it before you begin so you're not scrambling with water running. Reopen the main slowly to avoid a pressure surge, and if you can't find or turn the main shutoff, this is a quick job for a plumber.

Shut off the main, open the highest and lowest taps in the house to drain all the water (and the air-filled chambers refill with air), then close the taps and slowly restore the main. If the hammer returns, install a water-hammer arrestor at the supply valves nearest the offending fixture or appliance.

  1. Find and close the main water shutoff. Note the flooding risk if you can't locate it — do not start until you know where it is.
  2. Open the highest tap in the house (an upstairs faucet) and the lowest (a basement laundry tap or an outside bib) and let everything drain fully — this empties the waterlogged chambers so they refill with air.
  3. Flush each toilet once while draining to clear the tanks, then close all the taps you opened, starting from the lowest.
  4. Slowly reopen the main and let the system refill; the air trapped in the chambers should now cushion the shock. If the bang comes back within days, the home likely lacks working chambers — install a water-hammer arrestor at the culprit valve instead.
schedule30 min savings$0–40
Water-hammer arrestorMatch the connection (screw-on hose-bib type for washers, or a tee/stub-out type for a fixture) to where you're installing it
gavel Check your province first AB: homeowner may do this · BC: homeowner may do this · ON: homeowner may do this · PE: homeowner may do this · QC: licensed professionals only
Draining to recharge air chambers and adding a screw-on arrestor are generally owner-permitted; confirm the provincial rule. A pressure-reducing valve on the main routes to a licensed plumber.

verifiedWhy this one goes to a pro

You can measure your pressure with a cheap gauge, but correcting it is not a homeowner fix. A pressure-reducing valve installs on the main supply and has to be sized and set correctly — get it wrong and you either don't solve the hammer or you starve the whole house of flow. If your reading is well above the normal residential range, have a licensed plumber install or adjust the PRV.

Your notes travel with the request — what you saw, what you ruled out, when it started — so the pro arrives with a head start instead of a mystery.

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Why the list is in this order

We don’t sort by likelihood alone. We sort the way a good, honest tradesperson thinks: rule out the free, safe, common causes first. That’s why the cheap checks outrank the expensive repairs — and why anything dangerous gets a hard stop instead of a pep talk. The order exists to save you money, not to sell you anything.