Is water hammer dangerous or just annoying?

Both, eventually. Each bang is a pressure spike that fatigues joints, valves and flexi hoses over time. Left alone for years it can loosen fittings and contribute to leaks or burst connections, so it is worth fixing before it graduates from noise to damage.

Why do my pipes only bang when the washing machine runs?

Washing machines fill through solenoid valves that snap shut in milliseconds, which creates the sharpest shock wave in the house. A screw-on arrestor fitted between the laundry tap and the machine hose usually silences it.

Where does a water hammer arrestor need to go?

As close as possible to the valve causing the shock. For washing machines and dishwashers that means at the tap the hose connects to. Fitting one far away still helps a little, but proximity is what makes it effective.

Will lowering my water pressure stop the banging?

Often it makes a big difference. If your mains pressure is above 500 kPa, a pressure limiting valve reduces the force behind every spike and protects taps, hoses and appliances at the same time. Combined with secure pipe fixing, it resolves most cases.

Why did water hammer suddenly start when nothing changed?

Something usually did change quietly: mains pressure in the street increased, an ageing pressure limiting valve failed, a pipe clip let go inside a wall, or a new appliance with a fast solenoid valve joined the house.

Is water hammer dangerous or just annoying?

Both, eventually. Each bang is a pressure spike that fatigues joints, valves and flexi hoses over time. Left alone for years it can loosen fittings and contribute to leaks or burst connections, so it is worth fixing before it graduates from noise to damage.

Why do my pipes only bang when the washing machine runs?

Washing machines fill through solenoid valves that snap shut in milliseconds, which creates the sharpest shock wave in the house. A screw-on arrestor fitted between the laundry tap and the machine hose usually silences it.

Where does a water hammer arrestor need to go?

As close as possible to the valve causing the shock. For washing machines and dishwashers that means at the tap the hose connects to. Fitting one far away still helps a little, but proximity is what makes it effective.

Will lowering my water pressure stop the banging?

Often it makes a big difference. If your mains pressure is above 500 kPa, a pressure limiting valve reduces the force behind every spike and protects taps, hoses and appliances at the same time. Combined with secure pipe fixing, it resolves most cases.

Why did water hammer suddenly start when nothing changed?

Something usually did change quietly: mains pressure in the street increased, an ageing pressure limiting valve failed, a pipe clip let go inside a wall, or a new appliance with a fast solenoid valve joined the house.

Guides

Why are my pipes banging? Water hammer explained

By Terry, licensed plumber (Lic L10959) · 8 April 2026 · 4 min read

Quick answer

Banging pipes are usually water hammer: a pressure shock wave created when a fast-closing valve, typically in a washing machine, dishwasher or mixer tap, stops water suddenly. Loose pipe clips and high mains pressure make it worse. A water hammer arrestor or pressure limiting valve fitted by a plumber usually solves it.

Why are my pipes banging? Water hammer explained - Terry's Plumbing, Berala

That bang from the laundry wall when the washing machine stops filling is not the house settling. It is water hammer, a pressure shock wave that rips through the pipework when fast-moving water is forced to stop almost instantly.

Water is heavy and it does not compress. When a valve snaps shut, the moving column of water slams into it and the energy has nowhere to go, so it hammers back through the pipes as a spike of pressure. Plumbers call it hydraulic shock. That spike can briefly reach several times normal mains pressure, which is why the noise carries across the whole house.

Why modern appliances set it off

Washing machines and dishwashers fill through solenoid valves that close in milliseconds, which makes them the most common trigger by far. Single-lever mixer taps flicked off quickly do the same thing on a smaller scale. Older spindle taps close gradually as you wind them down, which is why water hammer only became widespread once modern appliances arrived.

Three ingredients make it worse

A fast-closing valve to create the shock in the first place.
High mains pressure. Anything above 500 kPa amplifies every spike, and plumbing standards require pressure that high to be limited anyway.
Loose pipework. Unclipped pipes move with each spike and knock against studs and joists, turning a pulse into a bang.

The fixes that actually work

A water hammer arrestor is a small sealed cushion of air or gas fitted near the offending valve; the shock compresses the cushion instead of slamming the pipe. Screw-on versions fit between the laundry tap and the washing machine hose in minutes. Where mains pressure is high, a pressure limiting valve at the meter calms the whole system rather than a single appliance. And where the noise is a rattle as much as a bang, securing loose pipe clips does more than any gadget, though access inside walls decides how practical that is. Terry pressure-tests the supply before fitting anything, because bolting an arrestor onto a system running at 700 kPa treats the symptom and leaves the cause in place.

Some older homes relied on vertical air chambers built into the pipework, and these waterlog over the years. Draining the whole system so the pipes refill with air can recharge them, but the relief is usually temporary.

Why it should not be ignored

Every bang is a pressure spike hitting joints, valves and flexible hoses. Repeated thousands of times, those spikes fatigue fittings, loosen joints and stress the braided flexi hoses under sinks, which fail spectacularly when they go. Water hammer is one of those problems that stays merely annoying right up until it becomes destructive, and the destructive stage never books an appointment.

Treat the noise as information. Find the fast-closing valve, check the mains pressure, secure the pipework, and the house goes quiet again.

Frequently asked questions

Is water hammer dangerous or just annoying?: Both, eventually. Each bang is a pressure spike that fatigues joints, valves and flexi hoses over time. Left alone for years it can loosen fittings and contribute to leaks or burst connections, so it is worth fixing before it graduates from noise to damage.
Why do my pipes only bang when the washing machine runs?: Washing machines fill through solenoid valves that snap shut in milliseconds, which creates the sharpest shock wave in the house. A screw-on arrestor fitted between the laundry tap and the machine hose usually silences it.
Where does a water hammer arrestor need to go?: As close as possible to the valve causing the shock. For washing machines and dishwashers that means at the tap the hose connects to. Fitting one far away still helps a little, but proximity is what makes it effective.
Will lowering my water pressure stop the banging?: Often it makes a big difference. If your mains pressure is above 500 kPa, a pressure limiting valve reduces the force behind every spike and protects taps, hoses and appliances at the same time. Combined with secure pipe fixing, it resolves most cases.
Why did water hammer suddenly start when nothing changed?: Something usually did change quietly: mains pressure in the street increased, an ageing pressure limiting valve failed, a pipe clip let go inside a wall, or a new appliance with a fast solenoid valve joined the house.

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