Water Hammer: Why Pipes Bang

Quick answer:

• Water hammer happens when a tap or valve closes too fast, sending a pressure shockwave back through your pipes
• DIY fixes include draining the system to recharge air chambers and checking your supply pressure
• Requirements can vary by property and authority. We will help you confirm what applies before work begins.
• If the banging keeps coming back, a plumber needs to install a water hammer arrestor or pressure limiting valve

Water hammer is a hydraulic shock that happens when fast-moving water is suddenly stopped or forced to change direction. It’s the loud banging, thudding, or rattling noise you hear inside your walls. Most cases can be sorted without a plumber, but persistent water hammer in Sydney homes often points to a pressure problem.

What is water hammer and why does it happen?

Think of it this way. Water flows through your pipes at speed. When you snap a tap shut, all that momentum has nowhere to go. The water slams into the closed valve and sends a shockwave back through the pipe. That’s the bang.

The technical term is hydraulic shock. Same principle as a low-speed car crash: the sudden stop transfers a lot of force into whatever’s in the way.

Water hammer gets worse when:

• Your water pressure is high (more on this below)
• Your pipes are long or have a lot of bends
• You have fast-closing solenoid valves, like those in washing machines and dishwashers
• Your pipes aren’t properly secured and physically move when the shock wave hits

Older homes in Hurstville, Kogarah, and Bexley often have copper pipe runs that weren’t clipped often enough. When those pipes are free to flex, even moderate water hammer makes a surprisingly loud noise.

What are the most common water hammer causes?

Fast-closing appliances

Modern washing machines, dishwashers, and some toilet fill valves use solenoid valves that snap shut almost instantly. Unlike a tap you turn by hand, these give the water no warning. The shock is sharper because of it.

If the banging always happens when your washing machine finishes filling, or right after your toilet refills, the appliance valve is almost certainly the culprit.

High water pressure

Sydney Water supplies mains water at varying pressures across the network. Properties on high-pressure mains, or homes at the bottom of a hill, can receive supply pressure well above comfortable levels. Parts of Sydney’s south, including areas around Sutherland and Cronulla, are known for higher supply pressures.

Requirements can vary by property and authority. We will help you confirm what applies before work begins. If your home’s pressure exceeds that, you’re required to have a pressure limiting valve (PLV) fitted. High pressure makes water hammer dramatically worse because there’s simply more force behind each shockwave.

We’ve also written a detailed post on high water pressure in Sydney homes if you want to go deeper on that problem specifically.

Waterlogged air chambers

Older Sydney homes were plumbed with air chambers: short vertical pipe sections installed near taps and valves, designed to trap a pocket of air that absorbs the shockwave. Over time, water dissolves that air and the chamber fills up. Once the air is gone, there’s nothing left to cushion the blow.

If your home was built before the 1980s, there’s a good chance it has air chambers in the system. They just need to be recharged.

Loose pipes

If the pipes aren’t secured tightly to the framing, they’ll physically move when water hammer hits. That movement creates secondary banging as the pipe slaps against timber or masonry. It’s a separate problem from the shockwave itself and has its own fix.

How to fix water hammer yourself

1. Drain the system to recharge air chambers

This is the best free fix for older homes with existing air chambers. Here’s how:

1. Turn off the main water supply at the stopcock (usually near your water meter at the front of the property)
2. Open every tap in the house, starting from the highest point and working down
3. Flush every toilet
4. Let the system drain completely
5. Turn the main supply back on slowly and let it refill
6. Close the taps once water runs steadily

As the water refills, it pushes air back into the chambers. You’ll often notice the improvement straight away. The fix usually lasts 12 to 18 months before the air gets absorbed again.

2. Check your water pressure

We inspect the job and confirm the price before work begins. Screw it onto an outdoor tap or laundry tap and turn it on fully. A reading above 500kPa means you almost certainly need a PLV. Anything between 350kPa and 500kPa is within the legal range but on the high side.

In Sydney’s south, readings of 600kPa or more without a PLV are not uncommon. That’s both a code compliance issue and a very likely cause of your water hammer.

3. Secure loose pipes

If you can access the pipe runs in a subfloor, roof space, or exposed laundry wall, check whether the pipe clips are intact and whether there’s any visible movement when water is running. Requirements can vary by property and authority. We will help you confirm what applies before work begins.

When DIY isn’t enough: fixes

The steps above sort most water hammer cases. If the banging continues, or your pressure is over 500kPa, you need a licensed plumber.

Water hammer arrestors

A water hammer arrestor is a sealed device with an internal air chamber separated from the water by a piston or diaphragm. Unlike a traditional air chamber, it doesn’t waterlog over time. Arrestors are fitted close to the problem source, typically at the washing machine connection, dishwasher, or toilet.

We inspect the job and confirm the price before work begins. Most homes need one or two.

Pressure limiting valves

A PLV is fitted at the water meter or main entry point and reduces incoming pressure to a set level, usually somewhere between 350kPa and 500kPa. We inspect the job and confirm the price before work begins.

Requirements can vary by property and authority. We will help you confirm what applies before work begins. It’s not optional. A PLV also extends the life of your taps, hot water system, washing machine hoses, and every other pressurised fitting in the house.

Replacing fast-closing valves

Some washing machine inlet valves can be swapped for slow-close versions. Your plumber can also fit mini water hammer arrestors directly behind appliance connections. Worth doing when the banging is isolated to one appliance and you’d rather not run a full PLV job.

Water hammer fix options at a glance

Does water hammer damage pipes?

Yes, over time. A single bang won’t burst a pipe, but repeated shockwaves fatigue joints, stress solder connections, and crack older fittings. Galvanised and older copper pipes (still common in pre-1970s homes across Rockdale, Bexley, and Ramsgate) are more vulnerable because the fittings have already had decades of wear.

The usual pattern: small leaks develop at joints months or years after the water hammer starts. You hear a bang for a year, ignore it, then find a damp patch inside a wall. At that point you’re dealing with water leak detection on top of everything else.

It’s cheap to fix early. It’s not cheap to fix after the wall comes open.

When to call a plumber for water hammer repair

Call a plumber if:

• The banging keeps coming back after you’ve drained and recharged the system
• Your pressure reading is above 500kPa
• The banging is happening in multiple spots around the house
• The noise has been getting louder or more frequent
• You’ve spotted damp patches near pipe runs

EKORP services Sutherland Shire, St George, and Georges River, including Cronulla, Miranda, Caringbah, Hurstville, Kogarah, Rockdale, and surrounding suburbs. Our general plumbing service covers water hammer diagnosis, arrestor installation, and PLV fitting.

Callout charges are confirmed before booking. 24/7 emergency response. On-site within 30 minutes. Call 02 8667 5354 or book online.

Frequently asked questions

What is the fastest water hammer fix I can try today?

Drain your system: turn off the main supply, open all taps from top to bottom, flush every toilet, then slowly refill. This recharges the air chambers and fixes most cases immediately at zero cost.

Is water hammer dangerous?

It won’t burst a pipe straight away, but repeated shockwaves stress pipe joints over time and cause leaks. Requirements can vary by property and authority. We will help you confirm what applies before work begins.

How much does it cost to fix water hammer in Sydney?

We inspect the job and confirm the price before work begins.

Can high water pressure cause water hammer?

Yes. Pressure above 500kPa makes water hammer significantly worse because there’s more force behind each shockwave. Properties in parts of Sydney’s south can receive supply pressure well over 500kPa. Requirements can vary by property and authority. We will help you confirm what applies before work begins.

Why does my washing machine make a banging noise in the wall?

Washing machines use solenoid valves that close almost instantly, creating a sharp hydraulic shockwave. A water hammer arrestor fitted to the washing machine inlet connection sorts this. We inspect the job and confirm the price before work begins.