A young couple in Edmondson Park rang about a bang in the wall of their two year old townhouse. Every time the washing machine finished filling, something in the laundry wall hit like a hammer, hard enough to rattle the frames in the hallway. They had been told it was normal for a new house. It is not. It is water hammer: the washing machine's solenoid valve slamming shut on a supply running at about 750 kPa, with a length of unclipped pipe in the wall doing the drumming.
Water hammer is the sharp bang or knock you hear when a tap, an appliance or a toilet shuts off. The fix is usually one of three things: bring the pressure down to 500 kPa with a pressure limiting valve, fit a water hammer arrestor next to whatever is slamming shut, or clip the pipe that is moving. We are a licensed plumber, no call-out fee, across South West Sydney.
Water hammer is the shock wave from a column of water stopped dead by a fast closing valve, usually a washing machine, dishwasher, mixer tap or toilet. Fit screw on arrestors at the washing machine taps, check your pressure with a gauge, and clip any pipe you can see moving. If the pressure is over 500 kPa or the bang is inside a wall, a plumber fits a pressure limiting valve or an arrestor at the source.
What water hammer actually is
Water is heavy and it does not compress. When a tap is open, the column of water between the meter and that tap is moving. Shut the tap slowly and the column slows with it. Shut it in a fraction of a second and the column stops dead, and all that momentum turns into a pressure spike that bounces back up the pipe as a shock wave. The pipe jumps, and if it can move at all it hits whatever is next to it: a stud, a noggin, another pipe, the back of the plasterboard. That is the bang. The wave travels the whole house, which is why a tap in the kitchen can knock in a bedroom wall.
Old screw down taps close slowly, so the houses in Fairfield and Cabramatta with original tapware rarely hammered. Modern homes are full of things that close instantly: washing machine and dishwasher solenoid valves, quarter turn mixers, some toilet inlet valves, fridge water lines. Add high mains pressure and pipes that were clipped loosely or not at all, and you get the Edmondson Park townhouse.
Why banging pipes matter
Noise is the least of it. Every hammer is a pressure spike well above normal working pressure, and the pipe joints, flexi hoses, appliance valves, mixer cartridges and the relief valve on the hot water system all take that hit, dozens of times a day. A pipe loose enough to bang is also rubbing on something, and copper rubbed against a bracket for ten years wears through. Most of the mystery leaks I find in walls around Liverpool started life as a noise someone got used to.
Pressure is the multiplier. The plumbing standard, AS/NZS 3500.1, caps static pressure at any outlet inside a building at 500 kPa, and above that a pressure limiting valve is supposed to bring it down. Sydney Water only guarantees a minimum of 15 metres of head at the property, but its own pressure management figures show the network averages about 52 metres, most properties sit between 15 and 65 metres, and some get more than 100 metres of head. A metre of head is roughly 10 kPa. So it is common around the low lying parts of Liverpool and Casula to find 600 kPa or more at the meter, well above what the fittings inside are designed for, and at that pressure every fast closing valve becomes a hammer.
Is it water hammer, or another kind of noisy pipe?
| The noise | When it happens | Likely cause | Fix |
|---|---|---|---|
| Single sharp bang or knock | The instant a tap, washing machine or toilet shuts off | Water hammer: fast closing valve, high pressure, loose pipe | Arrestor, pressure limiting valve, clip the pipe |
| Rapid rattle or chatter | While a tap is running, often part open | Worn tap washer or loose jumper valve fluttering in the flow | New washer or jumper valve |
| Humming or vibrating drone | While water runs anywhere in the house | Failing pressure limiting valve, worn toilet inlet valve | Replace the valve, check the pressure |
| Ticking or creaking | After hot water has run, as it cools | Hot pipe expanding and contracting against timber | Sleeve or re-clip the pipe, usually harmless |
| Squeal or whistle | When one tap or the toilet fills | Restricted valve, worn washer, part closed isolation tap | Open the tap, replace the washer or valve |
| Gurgling from drains | After water drains away | Drainage venting or a blockage, not the supply | Clear or vent the drain |
Water hammer fix: what you can do yourself
- Measure the pressure. A screw on pressure gauge for a garden tap is cheap at any hardware store. Fit it to the tap nearest the meter with everything else off. Over 500 kPa and you have found the multiplier, and a pressure limiting valve is the real fix.
- Fit arrestors at the washing machine. Small screw on water hammer arrestors go between the washing machine taps and the hoses. Five minutes with a shifter, and for washing machine water hammer on reasonable pressure it is usually the whole cure.
- Turn the appliance taps back a little. Slowing the flow to the washing machine softens the shut off. It is a band-aid, not a fix, but it tells you if you are on the right track.
- Clip what you can reach. If a pipe under the house, in the roof or in the laundry cupboard moves when the noise happens, secure it with proper saddle clips. Do not wedge it with a bit of timber. The rub point becomes the leak point.
- Replace chattering tap washers. If the noise is a rattle while the tap runs, a new washer and a look at the jumper valve is legitimate DIY, and how to fix a leaking tap covers the same job.
You will read online about draining the system to recharge the air chambers. Australian houses are rarely plumbed with air chambers, so skip it.
What a plumber does about pipes banging when a tap is turned off
If the gauge reads over 500 kPa, I fit a pressure limiting valve after the meter, which protects everything in the house, not just the noisy bit. If you have a continuous flow gas hot water unit I check its minimum pressure first, so the shower does not go cold in winter. That trade off is covered in low water pressure: causes and fixes. For a washing machine or dishwasher that still hammers, or a mixer tap or toilet that knocks, I fit a proper water hammer arrestor as close as possible to the valve that is closing: a sealed piston or bladder unit that absorbs the spike instead of letting it bounce around the house. Toilets get the arrestor at the isolation tap.
For the pipe in the wall, I find it. Sometimes that is a ceiling access, sometimes a small cut in the plasterboard behind the appliance, and the fix is clips and a bit of lagging so it cannot move again. On a renovation or new build I clip everything to the standard and put arrestors in before the wall is closed, because it is a ten minute job then and a half day job later. All of that is water plumbing work, which in NSW must be done by a licensed plumber. Done right. Done once.
What it costs
An arrestor at the washing machine taps or a pressure limiting valve at the meter is quoted on inspection, because the part, the pipe material and the access decide it, and an in-wall arrestor takes longer than one on the laundry taps. For labour, Sydney 2026 price guides put plumbers at $92 to $230 an hour, most around $140, with call-out fees of $69 to $170, and a tap washer or jumper valve repair at $92 to $300. Water hammer is never an after-hours job. Book it for business hours and you pay the day rate.
When to call a plumber
Call when the arrestors and clipping have not fixed it, when the gauge reads over 500 kPa, when the bang comes from inside a wall you cannot get to, when the noise arrived with a new tap or appliance, or when you have noticed a damp patch, a dripping relief valve on the hot water unit or a flexi hose that has started to bulge, because those mean the hammer has already done damage. If you are mid renovation, get the pipework clipped and protected before the plasterboard goes on; see renovations and new builds.
Monarch Civil & Plumbing covers South West Sydney and the Macarthur region from Austral. If you need a plumber in Edmondson Park, a plumber in Fairfield or anywhere in between, the leaks and burst pipes page covers this side of the work, or ring 0455 222 292 and describe the noise. I can usually tell you what it is before I get there.
Related guides: low water pressure.
Need it sorted? Ring 0455 222 292 any hour or book online. Monarch Civil & Plumbing is a licensed plumber, no call-out fee for Liverpool, Campbelltown, Camden and Austral, quoted on inspection.
Emergency in Liverpool or Campbelltown right now?
Ring 0455 222 292 and Paul answers. emergency plumber Liverpool and emergency plumber Campbelltown say what to shut off while he is on the way; everywhere else within about 20 km of Austral the 24/7 emergency plumber page covers it. Same rate day or night, no call-out fee.
Frequently asked
What causes water hammer in house pipes?
A moving column of water stopped suddenly. When a fast closing valve shuts, the momentum of the water turns into a pressure spike that bounces back through the pipes, and any pipe that can move hits the framing next to it. Washing machine and dishwasher solenoid valves, quarter turn mixer taps and some toilet inlet valves are the usual triggers. High mains pressure and loosely clipped pipes make it much louder.
Does a water hammer arrestor really work?
Yes, when it is fitted close to the valve that is closing. An arrestor is a sealed piston or bladder with a cushion of air behind it that absorbs the pressure spike instead of letting it travel through the house. Screw on arrestors for washing machine taps are a genuine five minute DIY job. For a toilet, a mixer tap or a dishwasher, the arrestor usually goes on the isolation tap or in the wall.
Why do my pipes bang when the washing machine fills?
Washing machines use solenoid valves that snap shut in a fraction of a second, which is the perfect way to start a shock wave. On high mains pressure the bang can be loud enough to shake a wall. Fit screw on arrestors between the taps and the hoses first, and check your pressure with a gauge on a garden tap. Over 500 kPa, a pressure limiting valve at the meter is the proper fix.
Can water hammer damage pipes?
Over time, yes. Each bang is a pressure spike that loads the joints, flexi hoses, mixer cartridges and appliance valves, and a pipe that moves enough to knock is also rubbing on whatever it hits. Copper worn through on a bracket and split flexi hoses are both common results. A bang that has gone on for years is worth fixing before it turns into a leak inside a wall.
How much does it cost to fix water hammer?
Arrestors and pressure limiting valves are quoted on inspection, because the part, the pipe material and the access decide the price, and an in-wall arrestor takes longer than one on the laundry taps. For labour, Sydney 2026 price guides put plumbers at $92 to $230 an hour, most around $140, with call-out fees of $69 to $170. It is never an after-hours job, so book it in business hours.
Is high water pressure the reason my pipes are noisy?
Often. The plumbing standard caps pressure at outlets inside a building at 500 kPa, but Sydney Water's network averages about 52 metres of head and some areas get over 100 metres, which is close to 1,000 kPa at the meter. That much pressure makes every fast closing valve hammer and shortens the life of taps and appliances. A pressure limiting valve after the meter fixes the cause rather than the symptom.
Licensed plumber and drainer based in Austral, 13+ years in the trade, working across Liverpool, Fairfield and the Macarthur region. About Paul