Why Are Your Pipes Banging
When No Water Is Running?
A Sydney Plumber's Diagnosis.

A bang from inside your walls when no tap is running is one of those sounds that's easy to ignore the first time and hard to ignore by the third. Most Sydney homeowners assume it's nothing, or assume it's something unfixable, and put up with it for years.

It's neither. Banging pipes nearly always have a specific, identifiable cause — and most causes have a direct fix. This guide will walk you through how to pinpoint exactly what's happening in your plumbing, what you can address yourself, and what needs a licensed plumber before it turns into an expensive leak or fitting failure.

Identify Your Noise First

Before working through causes, narrow down the exact nature of the sound you're hearing. Different sounds point to different problems. Getting this right will save you time and money.

Water Hammer: What's Actually Happening

Water hammer is responsible for the majority of banging-pipe complaints we attend to across Sydney. Understanding what's physically happening makes the fix obvious.

Water moving through your pipes has momentum. When a tap closes or a solenoid valve shuts (as in a washing machine or dishwasher), that moving column of water stops instantly. The kinetic energy has to go somewhere — it converts into a pressure shockwave that travels back through the pipe. When the shockwave hits a bend, a tee, or the end of a pipe run, it rebounds with enough force to physically move the pipe against the surrounding wall framing. That's the bang.

The severity of water hammer is directly related to:

• How fast the water was moving (flow rate and velocity)
• How abruptly the flow was stopped (solenoid valves are worse than quarter-turn ball valves, which are worse than screw-down tap spindles)
• How high the supply pressure is (higher pressure = faster water = bigger shockwave)
• Whether your system has any pressure cushioning (air chambers, arrestors)
• Whether pipes are secured (unsecured pipes amplify the movement)

All the Causes — and Their Fixes

• 01

  High Water Pressure

  The single most common root cause of water hammer in Sydney. Australian standards set the maximum allowable mains pressure at 500 kPa (roughly 72 PSI) at the meter. Many Sydney properties run significantly higher than this, particularly in low-lying areas or properties close to water storage facilities. High pressure forces water through pipes at greater velocity — and the resulting shockwave when flow stops is proportionally more powerful.

  You can test your pressure with a gauge attached to an outdoor tap. If it reads above 500 kPa, your property needs a pressure-reducing valve (PRV). Many Sydney properties had PRVs installed years ago — but PRVs have a service life of 8–12 years and can fail open, allowing pressure to rise again without the homeowner knowing.

  The fix

  Install or replace a pressure-reducing valve at the main. A correctly set PRV (typically 350–400 kPa) resolves water hammer across the entire property in one job. This is a licensed plumber job — not DIY.
• 02

  No Air Chamber or Water Hammer Arrestor

  Older Sydney homes (pre-1980s) were often built with simple air chambers — short vertical pipe stubs closed at the top — installed near taps and appliances. These act as a cushion: the shockwave from stopping water compresses the air in the chamber rather than slamming into a solid fitting. Over time, the air in these chambers gets absorbed by the water and the chamber fills with water, rendering it useless. The home now has no cushioning at all.

  Modern replacements are water hammer arrestors — sealed devices with a gas-charged chamber separated from the water by a piston. They don't waterlog, they don't need maintenance, and they're far more effective than traditional air chambers.

  The fix

  Install water hammer arrestors at the most affected connection points — typically behind the washing machine, dishwasher, and any solenoid-controlled valve. For whole-house protection, a PRV is more cost-effective than multiple arrestors.
• 03

  Unsecured or Loose Pipes

  Pipes that aren't firmly clipped to wall framing or joists can move when the pressure wave from water hammer hits them. The movement itself is what creates the banging — the pipe physically striking the surrounding structure. You'll often hear this as a series of knocks rather than a single thud, as the pipe bounces. It's particularly common in roof spaces and under floors, where pipes run long distances without adequate support.

  The issue is also common after renovation work where new walls have been built around existing pipes without proper securing. A pipe that previously had wall contact on both sides might now have a 300mm gap to the nearest stud.

  The fix

  A plumber locates the section of pipe responsible (usually identifiable by the location of the sound) and installs additional pipe clips or standoff brackets. Foam lagging between the clip and the pipe prevents any residual vibration from transmitting to the structure.
• 04

  Thermal Expansion of Copper Pipes

  Copper expands significantly with temperature changes — approximately 1.7mm per metre for every 10°C increase. In a Sydney home with 15 metres of copper hot water supply pipe, running a shower that raises the pipe temperature by 40°C will cause roughly 10mm of expansion across the run. When this expansion is restricted by a tight pipe clip or a close-fitting wall penetration, the pipe creaks and ticks as it forces its way through.

  The contraction as the pipe cools after use creates the same sound in reverse. This is why many homeowners notice ticking and creaking in their walls at night — as hot water use ends and pipes cool.

  The fix

  Pipe insulation reduces the temperature differential and therefore the magnitude of expansion. For significant cases, a plumber can replace rigid clips with expansion-allowing mounts, or install expansion loops in long runs to give the pipe room to move without transmitting stress to the structure.
• 05

  Trapped Air in Pipes

  Air pockets inside water pipes create a sharp thudding or cracking sound as water pushes them through bends or towards outlets. You'll typically notice this when you first turn on a tap — a series of spitting or banging sounds followed by normal water flow. It's common after any work on the water mains nearby (Sydney Water maintenance work will often introduce air into local pipe networks), after extended periods of no water use, or after isolation valves are shut and reopened.

  The fix

  Open the affected taps and let them run for 60–90 seconds. For whole-house air issues, open the highest tap in the house and the lowest simultaneously — this creates a pressure differential that helps push air through more efficiently. Most air issues self-resolve within a day. If they persist, there may be a slow leak introducing air into the system, which needs investigation.
• 06

  Worn Tap Washers or Valve Seats

  A worn washer inside a tap spindle doesn't seal cleanly against the valve seat. As water pressure pushes through the imperfect seal, the washer can flutter or vibrate — creating a rhythmic buzzing or banging sound that travels through the tap body and into the pipe. You'll often hear this when a tap is nearly closed but not fully shut, or when water pressure is high. It can also sound like a loud hum rather than a bang.

  Solenoid valves in washing machines and dishwashers suffer the same issue when the valve diaphragm degrades — you'll hear a sharp knock every time the cycle switches water on or off.

  The fix

  Replacing the washer is a straightforward job on traditional tap spindles. If the valve seat itself is worn or pitted, it needs reseating or replacing. Worn solenoid valves in appliances typically require the appliance's service technician rather than a plumber.
• 07

  Partially Closed Isolation Valves

  An isolation valve that is only partly open restricts water flow and creates turbulence as water forces its way through the reduced opening. This turbulence causes the pipe to vibrate — often described as a vibrating or rattling hum that's constant while water is running. Check isolation valves under sinks, behind toilets, and on the water supply to appliances — they should always be either fully open or fully closed, never halfway.

  The fix

  Locate and fully open any partially closed isolation valves. If a valve needs to be partially restricted for flow control, it's the wrong type of valve for that location — a plumber can replace it with an appropriate pressure-balancing fitting.
• 08

  Pressure Fluctuations from the Mains

  Sydney Water's distribution network can experience pressure surges — particularly overnight when demand drops across the network and mains pressure rises. If your property lacks a PRV, or has a failed one, these surges pass directly into your internal pipes. You may hear a single thud or creak at 2–3am with no water running — that's the surge hitting your system. Properties at the bottom of hills or close to pumping stations are most affected.

  The fix

  A properly sized and set pressure-reducing valve eliminates mains pressure fluctuations from reaching your internal plumbing. If you already have a PRV, have it tested — a failed PRV can allow full mains pressure through regardless of its setting.

Water Pressure in Sydney: What the Numbers Mean

Water pressure is the thread connecting most pipe noise complaints. Here's a quick reference for what your pressure reading actually means:

You can buy a simple pressure gauge from a plumbing supply store for under $30 and attach it to an outdoor tap. Take readings at different times of day — pressure can vary significantly between peak hours and overnight.

What You Can Fix Yourself vs What Needs a Plumber

How to Stop It From Happening Again

Once you've resolved the immediate problem, a few simple habits will significantly reduce the chance of it returning.

Check your water pressure annually

A $30 pressure gauge and five minutes once a year tells you whether your PRV is still working correctly. If mains pressure in your area has increased (not uncommon as Sydney Water upgrades its network), your PRV may need recalibration or replacement.

Service isolation valves every few years

Quarter-turn ball valves under sinks and behind toilets can seize partially open through infrequent use. Turn them to fully closed and back to fully open annually to keep them free and ensure they're always in the correct position.

Don't ignore small noises

A tap washer that creates a small buzz today creates a full rattle in six months and a stripped valve seat in twelve. Minor plumbing noises are early warning signs. They're cheap to fix when caught early and expensive when left.

Know your pipe material

Older Sydney homes with copper pipes experience more thermal expansion noise than modern homes with CPVC or PEX. If your home was built before the 1980s and you're hearing significant creaking, insulating the exposed pipe runs in roof and sub-floor spaces makes a noticeable difference.

Plan for appliance connections before installation

If you're installing a new washing machine or dishwasher, ask the installer (or your plumber) to fit a water hammer arrestor at the connection point. This is a $50–$80 add-on that prevents years of banging. Much easier to do at installation than to retrofit later.

Frequently Asked Questions