That sudden bang, thud, or rattling from inside your walls when you turn off a tap or appliance is one of the most startling sounds a home can make. It's called water hammer, and while it can sound alarming, it's a common plumbing problem in New Zealand homes — and often fixable. Left untreated, though, it can damage pipes, fittings, and appliances over time.
What Is Water Hammer and Why Does It Happen?
Water hammer occurs when fast-moving water is suddenly stopped or forced to change direction. The momentum of the water has nowhere to go, so it creates a pressure shockwave that travels back through your pipes — producing that characteristic bang or series of knocks.
Several things make NZ homes particularly prone to it:
- High mains water pressure — many NZ properties receive mains pressure well above the comfortable range for household plumbing
- Modern solenoid valves in dishwashers, washing machines, and toilets that snap shut almost instantly
- Copper or rigid PVC pipework that transmits shockwaves efficiently
- Loose or unsupported pipes that physically knock against framing or joists
Common Symptoms and What They Mean
| Symptom | Likely Cause |
|---|---|
| Single loud bang when tap is turned off | Classic water hammer from fast valve closure |
| Banging when washing machine fills or drains | Solenoid valve slamming shut |
| Rattling or ticking during flow | Loose pipe clips or thermal expansion |
| Repeated knocking after flushing toilet | Faulty fill valve or high pressure |
| Banging throughout the house | Very high mains pressure |
How to Diagnose the Problem Step by Step
Step 1: Identify when it happens
Note exactly which fixture or appliance triggers the noise. Turn taps on and off slowly versus quickly — does the bang change? This tells you whether it's pressure-related or valve-related.
Step 2: Check your water pressure
High mains pressure is one of the most common culprits in NZ. You can hire or buy a simple pressure gauge that screws onto an outdoor tap (available at Bunnings or Mitre 10). Normal household pressure should sit between roughly 200–350 kPa. If yours is reading significantly higher than this, pressure is likely contributing to the problem.
Step 3: Check for loose pipes
Head to your subfloor, ceiling space, or anywhere pipes are accessible. Gently push on visible pipes — do any move freely or rattle against timber? Loose pipes amplify water hammer significantly.
Step 4: Locate your pressure-limiting valve (PLV)
Most NZ homes built or replumbed in recent decades have a pressure-limiting valve (also called a pressure-reducing valve) installed near the toby (water meter). Check whether yours is present and functioning. A failed PLV can allow dangerously high pressure into your system.
Step 5: Check appliance hoses
Inspect the fill hoses on your washing machine and dishwasher. Kinked or poorly routed hoses can worsen the hammer effect from solenoid valves.
What You Can Safely Fix Yourself
Some water hammer remedies are straightforward DIY jobs:
Secure loose pipes
If you can access the pipes, adding or tightening pipe clips (saddle clips) is a simple fix. Use the correct size for your pipe diameter and fix them to solid timber framing. Clips are inexpensive and available at any hardware store.
Fit a washing machine arrestor
A water hammer arrestor is a small device that screws onto the water supply connection behind your washing machine or dishwasher. It contains a sealed air chamber that absorbs the shockwave when the solenoid valve closes. These are a homeowner-friendly fix — no special tools required.
Drain and recharge air chambers
Older homes sometimes have air chambers — short vertical pipe stubs near fixtures that act as cushions. Over time, water can waterlog these chambers. To recharge them:
- Turn off the main water supply at the toby
- Open all taps in the house to drain the system
- Turn the supply back on slowly — air will re-enter the chambers
Slow down tap closure
Get into the habit of closing taps gradually rather than snapping them shut. It sounds simple, but it genuinely reduces hammer in many cases.
Fixes That Require a Licensed Plumber
Plumbing work in NZ is regulated, and certain tasks must be carried out by a licensed plumber. Under the Plumbers, Gasfitters and Drainlayers Board (PGDB) rules, any work that involves connecting to or modifying your water supply pipework is restricted work and must be done by a registered tradesperson.
This includes:
- Installing or replacing a pressure-limiting valve (PLV) — essential if your pressure is too high
- Installing water hammer arrestors into the pipework (as opposed to screw-on hose fittings)
- Replacing faulty tap valves or toilet fill valves that are causing rapid closure
- Rerouting or re-supporting pipework inside walls or under floors where connections are involved
Attempting restricted plumbing work yourself can void your home insurance and create liability issues if something goes wrong. Always use a licensed plumber for these jobs.
How to Prevent Water Hammer Recurring
- Have a plumber check and set your PLV to an appropriate pressure — this single fix resolves water hammer in a large number of NZ homes
- Install water hammer arrestors at washing machine and dishwasher connections as a matter of course
- Ensure all pipework is properly clipped at regular intervals as per good trade practice
- When renovating, ask your plumber about flexible pipe connections for appliances, which absorb movement better than rigid fittings
- BRANZ research highlights that good pipe support and correct pressure management are the most effective long-term solutions
When to Call a Professional
Call a licensed plumber promptly if:
- The banging is new or getting worse — this can indicate a failing PLV or developing fault
- You notice water pressure fluctuations alongside the banging
- There are signs of a leak — damp patches, staining, or mould near pipes
- The noise occurs throughout the whole house, suggesting a system-wide pressure problem
- You've tried the DIY fixes above and the problem persists
Water hammer that's ignored can eventually cause joint failures, pinhole leaks, and appliance damage — repairs that cost far more than a plumber's call-out. The MBIE Building Performance guidance on plumbing systems (Building Code clause G12) sets out the standards your plumbing should meet, including acceptable pressure ranges.
You can find qualified, local plumbers in your area through tradedirectory.co.nz — look for someone registered with the PGDB.
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