Quick Answer
Water hammer is a loud banging or thudding noise in pipes that occurs when water flow is abruptly stopped — typically when a tap is turned off quickly, a solenoid valve closes, or a dishwasher or washing machine finishes filling. In Melbourne homes, the most common fix is installing a water hammer arrestor ($30–$80 from Reece or Bunnings) or reducing the mains pressure to below 500 kPa. A licensed plumber can diagnose and fix persistent water hammer in 1–2 hours.
What Causes Water Hammer?
When moving water is suddenly forced to stop, its kinetic energy has nowhere to go — it slams against the closed valve or pipe end and creates a pressure spike, sometimes reaching 6–8 times the normal mains pressure. That shock wave travels back through the pipe and produces the characteristic bang or thud.
The most common triggers in Melbourne homes:
- Fast-closing solenoid valves — dishwashers, washing machines, and automatic irrigation systems all use solenoid valves that snap shut instantly, far faster than a hand-turned tap.
- Quarter-turn taps — modern ball valves and lever mixer taps close much faster than old ceramic disc taps. Renovating bathrooms with new tapware commonly introduces water hammer that wasn’t there before.
- High mains pressure — Melbourne’s mains water pressure can exceed 800 kPa in some suburbs, particularly on hills fed by high reservoirs. The higher the pressure, the more violent the shock wave.
- Air chambers depleted — older homes sometimes had air chambers (short capped pipe sections) installed to cushion pressure spikes, but these become waterlogged over time and lose their cushioning effect.
- Loose pipe brackets — pipes that rattle against walls or joists amplify the noise, making moderate hammer sound much worse than it is.
Diagnosing the Source
| Symptom | Most Likely Cause | Action |
|---|---|---|
| Bang when washing machine fills or drains | Solenoid valve on machine supply | Install hammer arrestor on inlet hoses |
| Bang when dishwasher fills | Dishwasher solenoid valve | Install hammer arrestor at under-sink supply |
| Bang when tap is turned off quickly | Fast-closing lever tap, high pressure | Fit flow regulator or slow-close valve; check mains pressure |
| Bang throughout house, multiple fixtures | Mains pressure too high (>500 kPa) | Have plumber install or adjust pressure limiting valve |
| Rattling/banging pipes but no specific trigger | Loose pipe brackets | Secure loose brackets; add foam pipe lagging at contact points |
| Ticking pipes after hot water use | Thermal expansion of pipes | Normal — not water hammer; insulate pipes if bothersome |
DIY Fixes for Water Hammer
Install a Water Hammer Arrestor
A hammer arrestor is a small device with a sealed air chamber and piston that absorbs pressure spikes. It installs inline on the supply pipe closest to the problem valve. Most come in standard 15mm or 20mm pipe thread sizes to suit Australian copper plumbing. Brands available at Reece and Mitre 10 include Fix-A-Tap alternatives.
For washing machines: most brands now sell hose sets with built-in arrestors. For dishwashers and irrigation: fit an arrestor at the supply angle stop or under-sink isolator.
Reduce Mains Pressure
Most Australian homes have a pressure limiting valve (PLV) fitted near the water meter. A plumber can adjust or replace the PLV in under an hour. Some Melbourne suburbs on elevated mains regularly see 600–800+ kPa at the meter — far above the 150–500 kPa recommended range.
Secure Loose Pipes
Check under sinks, in the roof cavity, and any exposed pipe runs for loose brackets or clips. A pipe vibrating against a joist dramatically amplifies water hammer. Use foam pipe lagging or rubber-lined clips to cushion contact points.
When to Call a Plumber
- Mains pressure exceeds 500 kPa and you need a PLV installed or adjusted
- Pipes are making noise inside walls or ceilings you cannot access
- Banging started after a plumbing renovation — incorrectly sized pipes can cause turbulent flow
- You notice water stains near noisy pipes — potential joint failure
Tips and Gotchas
- Start with a pressure check — 80% of water hammer cases are partly caused by high mains pressure. A $15 gauge saves diagnostic time.
- Hammer arrestors are sized by pipe diameter — most residential copper is 15mm; buy the right thread size.
- New quarter-turn taps after reno — slow-close quarter-turn taps are available and solve this without a PLV.
- Foam pipe lagging dampens noise — wrapping exposed pipes reduces audible impact even if hammer persists.
- Check your T&P valve — chronic high pressure causes it to drip repeatedly; have mains pressure checked urgently if this occurs.
- Older homes with air chambers — pre-1990 homes in Dandenong and Frankston can recharge air chambers by draining and slowly refilling the system.
- Irrigation solenoids are common culprits — add a hammer arrestor on each zone supply or use slow-close valves on the controller output.
FAQ
Is water hammer dangerous?
Occasional mild water hammer is mostly a nuisance. However, chronic severe water hammer can loosen soldered copper joints and eventually cause pinhole leaks or connection failures. High mains pressure also shortens the life of hot water systems, washing machine hoses, and tap cartridges. Fix it sooner rather than later.
Why did water hammer start after I installed a new washing machine?
Modern washing machines use fast-closing solenoid valves. If your mains pressure is above 400 kPa, the sudden valve closure creates a significant pressure spike. A washing machine hose set with built-in hammer arrestors (available at Reece or appliance stores) usually fixes this completely.
How much does it cost to fix water hammer in Melbourne?
A DIY hammer arrestor costs $30–$80 and takes 15–30 minutes to install. Professional diagnosis and repair typically costs $150–$350 for a licensed plumber visit, including PLV adjustment or arrestor installation. If the PLV needs replacement, expect $300–$500 all-inclusive.
My pipes bang only at night — why?
Mains water pressure rises at night when demand across the network drops. In Melbourne’s suburban areas, overnight pressure can be 100–200 kPa higher than during peak demand. A PLV set at 400–450 kPa will cap overnight pressure and eliminate the night-time banging.
Local Melbourne Resources
- Reece Plumbing — water hammer arrestors and pressure gauges at trade counters across SE Melbourne
- Bunnings — Water Hammer Products — Fix-A-Tap arrestors and foam pipe lagging in-store
- Victorian Building Authority — Find a Licensed Plumber — for PLV work and inaccessible pipe repairs
- Yarra Valley Water — Water Pressure Info — check typical pressures in your SE Melbourne suburb
- South East Water — covers Frankston, Mornington Peninsula and Cranbourne areas