Water hammer is a pressure shockwave that happens when fast-moving water is stopped suddenly — usually by a quick-closing tap, washing machine or dishwasher valve. The bang you hear is the pipe physically jolting, and over time it loosens joints, damages valves and can cause leaks or bursts. Persistent banging, humming or knocking pipes should be assessed by a licensed plumber.
What that bang actually is
Water moving through your pipes carries real momentum. When a valve snaps shut — a quarter-turn mixer tap, a washing machine solenoid, a dishwasher inlet — that moving column of water has nowhere to go and slams to a stop. The result is a pressure spike that can briefly reach several times your normal water pressure, and the bang you hear is the pipe jolting against the wall or its brackets.
Plumbers call it water hammer, and it's one of the most common noise complaints we get across Sydney homes — especially in houses with modern quick-closing tapware retrofitted onto older pipework.
Why it's more than an annoying noise
Every bang is a small shockwave physically stressing your plumbing. One knock won't hurt anything, but water hammer repeats every time the offending valve closes — dozens of times a day, year after year.
- ›Joints and fittings gradually work loose, leading to weeping leaks inside walls.
- ›Valves in appliances, toilets and hot water systems wear out early.
- ›Pipe brackets crack or pull free, letting pipes move and rub.
- ›In older or corroded pipework, the repeated pressure spikes can eventually cause a split or burst.
If banging has recently become louder or more frequent, take it seriously — it often means something has changed, like rising street pressure or a failing valve.
Common causes we find in Sydney homes
- ›Water pressure that's too high — many Sydney streets deliver well above the 500 kPa recommended for homes, which makes hammer worse and voids some appliance warranties.
- ›Quick-closing mixer taps and appliance solenoid valves stopping flow instantly.
- ›Pipes that were never properly clipped or have come loose from their brackets.
- ›Worn tap washers or a faulty toilet inlet valve — these can also cause humming, vibrating or machine-gun rattling sounds.
- ›Air chambers or arrestors that have become waterlogged and stopped absorbing the shock.
Diagnosing which of these is behind your noise takes a pressure test and a proper inspection — the fix for high street pressure is completely different from the fix for a loose pipe or a worn valve, and guessing wrong just moves the problem around.
When to call a plumber
Any persistent banging, knocking, humming or vibrating from your pipes is worth a professional look — especially if it's getting worse, if you've noticed pressure changes, or if your home has older pipework. Left alone, water hammer tends to end as a leak inside a wall, which costs far more to fix than the noise ever did.
Eagle Plumbing 24/7 can test your water pressure, find the source of the noise and fix it properly. We're licensed (NSW Licence 498336C), insured for $20M, charge $0 call-out on standard call-outs and back every job with a lifetime workmanship guarantee. Call 0489 998 221 — we're available 24 hours a day across Sydney, the Blue Mountains, Hawkesbury and the Illawarra.