Do your pipes make a loud bang or thump when you turn off a tap, flush the toilet or when the washing machine finishes filling?
You may be hearing water hammer.
Water hammer happens when moving water is forced to stop suddenly inside the plumbing system. The resulting pressure surge can travel through the pipes and create the distinctive banging noise you hear inside walls, beneath floors or near plumbing fixtures.
An occasional quiet knock is not always a major concern. Repeated or forceful banging, however, is worth investigating because it can place unnecessary stress on pipes, fittings, valves and connected appliances.
What Is Water Hammer?
Water travelling through a pipe has momentum. When a tap closes gradually, the flow slows before stopping. When a valve closes very quickly, the moving water is brought to an abrupt stop.
That sudden change creates a pressure wave inside the plumbing. The energy travels through the pipework and may cause pipes to move, valves to vibrate or fittings to produce a loud bang.
What Does Water Hammer Sound Like?
The most recognisable symptom is a sudden bang or knock and usually happens immediately after water flow stops.
You might hear it when:
you quickly turn off a tap
a washing machine finishes filling
a dishwasher valve closes
a toilet cistern stops refilling
a shower mixer is shut off
The noise may sound as though it comes from a different part of the house because the pressure wave can travel through the plumbing.
What Causes Water Hammer?
Water hammer is caused by a sudden change in water flow, usually when a valve closes quickly. The moving water has been stopped quickly, creating a pressure surge that travels through the plumbing.
Washing machines, dishwashers, toilets and fast-closing taps can all trigger it. High water pressure and loose pipework may make the problem worse.
Why Do Washing Machines and Dishwashers Cause Banging Pipes?
Washing machines and dishwashers are common water-hammer triggers because they use fast-closing valves.
When an appliance stops taking in water, the valve may shut almost instantly. That sudden stop can create a pressure surge in the supply pipe.
If you hear a bang at exactly the moment your washing machine or dishwasher finishes filling, that is a useful diagnostic clue.
Some toilet inlet valves and modern tapware can create a similar effect.
Can High Water Pressure Cause Water Hammer?
High water pressure can make water hammer more noticeable and potentially more severe. The stronger the flow before it suddenly stops, the greater the shock may be.
High pressure can also increase wear on:
valves
tapware
flexible hoses
appliance connections
hot water components
This is relevant in Wellington because properties at different elevations can experience very different water-pressure conditions.
If your pipes bang and your taps also seem unusually forceful, a plumber can test the incoming pressure and check whether pressure control is required.
Can Loose Pipes Make Water Hammer Worse?
Yes. Water hammer creates the pressure shock, but loose or poorly supported pipes can make the noise much louder.
When the water stops suddenly, a pipe may move and strike walls, nearby pipework, brackets or other building materials.
A plumber may therefore need to address both the pressure surge and the way the pipes are supported. The loudest point in the house is not always where the problem begins.
Can Water Hammer Damage Pipes?
Repeated water hammer can place extra stress on plumbing components.
Over time, pressure surges may contribute to wear on:
pipe joints
fittings
valves
seals
flexible hoses
appliance connections
One loud bang does not mean a pipe is about to burst. But if the pipes bang forcefully every time the washing machine runs, a toilet finishes filling or somebody shuts off a tap, it is worth finding out why.
Is Every Banging Pipe Water Hammer?
No. Several plumbing noises can sound similar.
Water hammer: Usually creates a sharp bang or thump when water flow suddenly stops.
Loose pipes: May rattle or knock as water starts, stops or changes direction.
Expanding hot water pipes: Pipes can tick or knock as they heat up and expand against framing or surrounding materials.
Hot water cylinder noises: Popping, rumbling or banging near the cylinder itself may have another cause.
Drain noises: Gurgling from waste pipes or drains is not water hammer.
The timing of the noise is one of the best clues. A distinct bang immediately after a tap or valve closes makes water hammer more likely.
How Do Plumbers Fix Water Hammer?
There is no single fix for every home. The first step is identifying what is triggering the pressure surge.
Possible solutions include:
Securing loose pipes: If pipework is moving and hitting surrounding materials, additional support may reduce the noise.
Checking water pressure: If the property has excessive pressure, a plumber can assess the pressure-control equipment and determine whether adjustment or repair is needed.
Repairing faulty valves: A worn or malfunctioning valve may be contributing to sudden changes in water flow.
Installing a water hammer arrestor: A water hammer arrestor is designed to absorb the shock created when moving water suddenly stops.
These devices are usually positioned near the valve or appliance causing the problem. The correct type and location depend on the plumbing system, so installing one randomly may not solve the issue.
Is Water Hammer More Concerning in an Older Wellington House?
Older Wellington homes can contain plumbing installed or modified at different times.
You may have a combination of:
ageing pipes
older valves
mixed pipe materials
previous repairs
pipework that is no longer well supported
older low-pressure hot water systems
Water hammer does not automatically mean the pipes need replacing.
However, persistent banging in a house with older plumbing is a good reason to have the overall system assessed rather than simply trying to silence the noise.
Stop Banging Pipes at the Source
Water hammer is more than an irritating sound. The bang can be a sign that water inside the plumbing is stopping abruptly enough to create a pressure shock.
The fix may involve securing loose pipes, replacing a faulty valve, controlling water pressure or installing a properly positioned water hammer arrestor. The important part is diagnosing why the pipes are banging before choosing the solution.
Maxey Plumbing & Gas can investigate noisy plumbing, water-pressure problems and ageing pipework across Wellington City, Lower Hutt, Upper Hutt and Porirua.
If your pipes bang every time a tap, toilet, dishwasher or washing machine shuts off, contact our team on 04 390 0135 to arrange an assessment.
Frequently Asked Questions About Water Hammer
Why do my pipes bang when the washing machine is running?
Washing machines use quick-closing inlet valves. When the machine stops filling, the valve can shut almost instantly and create a pressure surge.
If the bang consistently happens at that moment, water hammer is a likely cause.
Why do my pipes bang when the toilet finishes filling?
The toilet's inlet valve closes when the cistern reaches the correct water level. If the valve closes quickly, it can trigger water hammer.
Water pressure and the way nearby pipes are supported can affect how noticeable the bang becomes.
Can water hammer damage pipes?
Repeated water hammer can place additional stress on pipes, joints, valves and connected equipment.
It does not mean a pipe will immediately burst, but persistent hydraulic shock is worth correcting.
Will a water hammer arrestor stop banging pipes?
A correctly selected and positioned water hammer arrestor can absorb the pressure surge caused by a quick-closing valve.
However, banging can also be caused by loose pipes, high pressure or faulty valves, so the cause should be diagnosed first.
Should I call a plumber about water hammer?
If the banging is frequent, loud, getting worse or affecting several fixtures, having it checked is sensible.
You should also arrange an inspection if the noise is accompanied by leaks, unusually high pressure or visible pipe movement.
