Noisy Pipes And Water Hammer

A knock or a bang in the wall when a tap or an appliance shuts off gets tolerated for years. Residents learn to live with it and only report it when a neighbour complains.

It is worth fixing earlier than that, because the noise is a symptom of a force, and the force is doing damage.

What is actually happening

Water moving through a pipe has momentum. When a valve closes quickly, that moving column of water stops almost instantly, and the energy has to go somewhere.

It goes into a pressure spike that travels back along the pipe. That spike is what you hear when it hits a bend, a bracket or a fixed section of pipework.

Every time it happens, joints and fittings take the hit. It is a slow process, and the eventual failure looks like an ordinary leak rather than the end of a long sequence.

What makes it worse

Fast closing valves. Washing machine and dishwasher solenoids shut in a fraction of a second, which is why the noise is often loudest when an appliance fills. Modern tapware with ceramic disc cartridges closes faster than old washer taps too.

High supply pressure. A building on high mains pressure hammers harder than one on moderate pressure. It also wears every fitting in the building faster and increases the volume of any leak.

Loose pipework. A pipe that is not clipped properly is free to move, and it bangs against timber or masonry when the spike passes. Half of what people call water hammer is actually an unsecured pipe.

Long straight runs. More water in motion means more energy to absorb.

The fixes, in order of sensibility

Check the pressure first. If the incoming pressure is high, a pressure limiting valve at the supply solves the hammer and extends the life of everything downstream. It is the single best value repair in this list, and in a lot of buildings the existing limiting valve has simply failed and needs replacing rather than adding.

Then secure the pipework. Clipping loose runs where they are accessible removes the noise even where some spike remains.

Then fit arrestors near the offending fixtures. A properly rated water hammer arrestor absorbs the spike close to where it is created.

Air chambers in older systems waterlog over time and stop working. Draining the system down and refilling can restore them temporarily, which is why the noise sometimes disappears after unrelated work and comes back months later.

Other noises that are not hammer

A continuous hum or vibration while water runs is usually a valve partially closed or a worn washer.

A groan when a tap opens is often a tap washer that has hardened.

A rushing sound in a wall with no fixture running is worth attending to quickly, because that can mean water is moving somewhere it should not be.

In an apartment building

Pressure is usually a building level issue rather than an apartment one, which means the useful fix sits with the owners corporation rather than with an individual owner.

That is worth establishing early. An owner can replace tapware repeatedly and never address a supply pressure that is damaging fittings across the whole building.

A pressure test at the meter and at a few apartments gives a strata committee something concrete to act on.

What to report

Which fixture triggers it, whether it happens on opening or closing, and whether it has got worse.

We handle this under plumbing, and on a managed building we would start with the pressure rather than the noise. If residents are reporting banging pipes, let us test the supply first.