Water hammer is one of those faults people live with for years because it seems like a personality quirk of the house. It is not. It is repeated mechanical shock, and the things it eventually breaks, joints, valves and flexi hoses, are the things that flood houses.
Water hammer causes and fixes
| Cause | How to spot it | The fix | Cost guide |
|---|---|---|---|
| Mains pressure above 500 kPa | Bangs at multiple taps, aggressive flow, splashy taps | Pressure limiting valve (PLV) at the meter | Quote on inspection |
| Fast-closing valves (washing machine, dishwasher solenoids) | Bang when the appliance mid-cycle stops filling | Hammer arrestor at the appliance taps | Quote on inspection |
| Unclipped or loose pipework | Rattling or knocking, sometimes ongoing after the bang | Secure and clip accessible pipe runs | Quote on inspection |
| Quarter-turn taps and mixers replacing old taps | Hammer started after a tapware upgrade | Arrestors, PLV, or both | Quote on inspection |
| Ageing flexi hoses under stress | Not a cause, but the likely first casualty | Proactive replacement | $20 to $40 a hose at trade, plus fitting |
| Worn tap washers or jumper valves | Machine-gun rattle while a tap runs, not just at shutoff | Tap service | $80 to $180 plus parts |
What actually causes water hammer?
Water is heavy and does not compress. When it is moving through your pipes and a valve snaps shut, all that momentum has nowhere to go, so it becomes a pressure spike that can briefly multiply the static pressure, and the pipe jolts, hitting whatever timber it is near. Modern homes hammer more than old ones for two reasons. First, quarter-turn taps, mixers and appliance solenoid valves close almost instantly, where old-style taps closed gradually as you wound them down. Second, suburban mains pressure across parts of the Gold Coast runs well above the 500 kPa that AS/NZS 3500.1 sets as the maximum for new installations, and the higher the pressure, the faster the water is moving and the harder it stops. Add a pipe run that was never clipped properly inside a wall, and you get the full percussion section.
Is water hammer actually damaging my pipes?
Yes, cumulatively. Each bang is a mechanical shock to every joint, valve and fitting on the line, and the weakest links fail first. In our experience the most common casualty is the braided flexi hose under a sink or behind a toilet: already the most failure-prone item in a modern home, and repeated hammer shortens its life further. A burst flexi can put thousands of litres into a house in hours, which is why we replace suspect hoses proactively, at $20 to $40 a hose at trade prices plus fitting, while attending anything else. Persistent hammer also loosens joints, damages appliance inlet valves, and in the worst cases contributes to splits in older pipework, which lands you on our burst pipe page: accessible burst repairs run $250 to $650 plus parts. The noise is the polite warning phase.
How do I stop water hammer for good?
Match the fix to the cause, which is why we diagnose before quoting. If pressure is the driver, and a quick gauge test at your garden tap tells us, the durable fix is a pressure limiting valve at the meter, which drops the whole house to a sane pressure, protects every appliance and flexi in the building, and usually kills the hammer outright. Queensland already requires pressure control on new builds for exactly this reason; older Gold Coast homes simply never got one. If the hammer is specific to the washing machine or dishwasher, a small hammer arrestor fitted at those taps absorbs the spike from the solenoid valve. If the noise is more rattle than bang, accessible pipework may just need clipping. These jobs are quoted on inspection because access and cause vary house to house, and we quote fixed before any work starts. One honest note: arrestors screwed onto appliance taps as a DIY guess sometimes help, but if the underlying pressure is 700 kPa, they are treating the symptom while every other fitting in the house keeps copping it.
Why did water hammer suddenly start in my house?
Because something changed. New tapware or a new appliance introduced fast-closing valves. The water authority did works and local pressure rose. A pipe clip corroded and let go. Or a tap washer wore to the point of fluttering, which causes the distinctive machine-gun rattle while water is running rather than a single bang at shutoff; that one is a simple tap service at $80 to $180 plus parts. New hammer is a prompt worth acting on, because it often means pressure or a failing component has crossed a line.
What should I do right now?
Note which taps or appliances trigger the bang and whether it started recently. That plus a two minute pressure test when we arrive usually nails the cause on the first visit.
Sources: AS/NZS 3500.1 (maximum 500 kPa at outlets for new installations); Plumbing and Drainage Act 2018 (Qld); Queensland Development Code MP 4.1 water efficiency provisions.
Banging pipes driving you mad, or worried what they are doing to your plumbing? Call Hills Plumbing & Gas on 0472 657 042 or book through our Burst Pipe Repairs service page. Fixed-price diagnosis and repair, Gold Coast wide, QBCC licence 15243081.