How to Fix Water Hammer — Stop Banging Pipes in Your Walls

Learn what causes water hammer, how to install an arrestor, drain your system, and fix loose pipe straps to silence banging pipes for good.

That loud BANG that rattles through your walls whenever a washing machine shuts off or someone turns off a faucet quickly isn’t just startling — it can actually damage your plumbing over time. That noise has a name: water hammer (technically called hydraulic shock), and it’s a fixable problem.

The good news? Most water hammer issues can be resolved with one of three approaches, and the cheapest fix costs exactly nothing.

What Causes Water Hammer

Water moving through pipes has momentum. When a valve closes suddenly — like a washing machine’s solenoid valve or a faucet you snap off — that moving water slams into the closed valve. The energy has to go somewhere, so it creates a pressure spike that travels back through the pipe, making it jump and bang against wall studs, joists, or other pipes.

Modern plumbing codes require water hammer arrestors on appliances with quick-closing valves (dishwashers, washing machines, ice makers). But many older homes don’t have them, or the existing ones have failed because they’re actually just short vertical pipe sections (called “air chambers”) that have filled with water over time.

Step 1: Identify the Problem Source

Before grabbing tools, figure out which fixture or appliance is causing the bang:

1. Run each appliance and faucet one at a time.
2. Listen for the bang when water shuts off.
3. Note whether it’s one fixture (local problem) or every fixture (whole-house issue).

One fixture only: The problem is specific to that appliance or faucet. An arrestor at that location will usually fix it.

Multiple fixtures or random banging throughout the house: You may have a whole-house pressure issue or failed air chambers throughout the system.

Step 2: The Free Fix — Drain the System (Restore Air Chambers)

Many homes built before the 1990s have built-in air chambers — short vertical pipes near fixtures that trap air to cushion the shock. Over time, the air dissolves into the water and the chambers fill up, rendering them useless.

Restoring them takes five minutes:

1. Shut off the main water supply at the house shut-off valve.
2. Open the highest faucet in the house (usually a second-story bathroom sink) to let air in.
3. Open the lowest faucet (basement sink or outdoor spigot) and let the system drain completely until water stops flowing.
4. Leave all faucets open for 2–3 minutes to let air re-enter the pipes.
5. Close all faucets, turn the main water back on, and listen for the bang.

If the air chambers simply needed refilling, the hammer should be gone. This works about 40% of the time and costs nothing.

Step 3: Install a Water Hammer Arrestor

If draining the system didn’t fix it (or you have modern copper/pex plumbing without air chambers), install a mechanical water hammer arrestor at the problem fixture.

What you need:

• One or two water hammer arrestors ($10–$15 each at any hardware store)
• Adjustable wrench
• Teflon tape (pipe thread sealant)
• Towel (there will be some spillage)

For a washing machine (most common cause):

1. Turn off the hot and cold water supply valves behind the washing machine.
2. Disconnect the washing machine hoses from the supply valves.
3. Screw a water hammer arrestor onto each supply valve (one for hot, one for cold). Wrap the threads with Teflon tape first.
4. Reconnect the washing machine hoses to the top of the arrestors.
5. Turn the water back on slowly, check for leaks, and run a wash cycle.

For a dishwasher or ice maker:

These are usually harder to access but the principle is the same — install a single arrestor on the supply line just before the appliance’s shut-off valve. If you can’t reach the connection point easily, inline arrestors are available that splice into the existing supply line with compression fittings.

For individual faucets:

If a specific sink or toilet is causing the hammer, you can install a compact “angle stop” arrestor that replaces the existing shut-off valve under the sink or behind the toilet.

Step 4: Secure Loose Pipes

Draining the system and adding arrestors solves the pressure spike, but if the pipes are already loose inside the walls, they can still rattle. After you’ve addressed the water hammer at the source, check for loose pipe supports.

What to look for:

• Pipes that move when you push on them gently
• Banging that seems to come from a specific wall cavity or ceiling
• Pipes in an unfinished basement or crawlspace that aren’t secured to joists

How to fix it:

• In open areas (basement, crawlspace): Install pipe straps or pipe clips every 4–6 feet along the run. Use rubber-lined straps to reduce vibration noise.
• Inside finished walls: This is harder to fix without opening the drywall. A temporary option is to install foam pipe insulation in the gap around pipes where they pass through floor or ceiling penetrations.
• For copper pipes: Use copper pipe straps with rubber inserts. Metal-on-metal contact amplifies noise.

Step 5: Check Your Home’s Water Pressure

If you’ve tried everything above and pipes still bang — or you have hammer throughout the house — your water pressure may be too high. Residential water pressure should be between 40 and 60 PSI. Above 80 PSI, the force of the water alone can cause hammer, put stress on your fixtures, and even damage your water heater.

1. Buy a pressure gauge ($10–$15) that screws onto an outdoor spigot or washing machine valve.
2. Screw it on and turn the faucet on full — read the pressure.
3. If it’s above 80 PSI: You need a pressure reducing valve (PRV) installed at the main water line. This is usually a job for a plumber ($150–$300 installed), though handy homeowners can DIY it.

When to Call a Plumber

Most water hammer is fixable with the steps above. Call a pro if:

• You’ve tried draining the system, installing arrestors, and securing pipes — and the banging continues
• Your water pressure is above 80 PSI and you’re not comfortable installing a pressure reducing valve
• You hear banging from inside finished walls that you can’t access
• The banging is accompanied by water leaking from joints or fittings (this is an emergency — shut off the water and call immediately)
• You have galvanized steel pipes (common in pre-1960s homes) — these are more susceptible to water hammer damage and harder to work with

Preventing Future Water Hammer

• Install arrestors proactively when you buy a new washing machine, dishwasher, or ice maker
• Drain your plumbing system once a year as part of spring maintenance — this keeps air chambers topped up
• Don’t slam faucets shut — especially kitchen and bathroom faucets with ceramic disc cartridges, which are more sensitive to abrupt shut-off
• Check your water pressure annually — a $10 gauge test is cheap insurance

Bottom line: Water hammer is annoying and potentially damaging, but it’s almost always fixable. Start with the free fix (drain the system), move to hardware ($10–$30 in arrestors), and escalate to a pressure check if needed. In most homes, you’ll have quiet pipes in under an hour.