How to Stop Water Hammer in Your Pipes

Turned a tap on or off and heard a loud bang, knock or thud from the pipes? Maybe it's the washing machine or dishwasher setting off the racket. That's water hammer, and while it's startling, the bigger problem is that if you leave it, it can do real long-term damage to your pipes and fittings. Here's what it is, why it happens, and how to fix it.

What is water hammer?

Water hammer, or hydraulic shock, happens when fast-moving water suddenly hits a closed valve in your pipes. That creates a pressure surge, which is the loud hammering sound you're hearing. Over time, repeated spikes can loosen pipe joints, damage valves and even lead to burst pipes, so it's worth sorting properly.

What causes it?

A few common causes:

Fast-closing taps or valves. When a tap or appliance shuts off quickly, the sudden stop in flow sends a shockwave back through the pipes.

High water pressure. Excess pressure makes water hammer more likely.

Missing or faulty air chambers or arrestors. These absorb pressure surges, so if they're missing or failed, hammer becomes a problem.

Loose pipes. Pipes that aren't properly secured move around and amplify the banging.

How to stop water hammer

Let's work through the fixes, from the easiest up to the more involved.

1. Check and reduce your water pressure

This is the easiest fix. High pressure makes the shock worse, so:

• Check your pressure with a gauge (cheap at any hardware store).
• If it's above 500 kPa, fit a pressure-reducing valve (PRV) to bring it to a safer level.
• If you already have a PRV, it may need adjusting or replacing.

2. Secure loose pipes

Rattling, shaking pipes can set off water hammer too.

• Check under sinks, in the subfloor and behind walls where you can get to them.
• Use pipe brackets, clips or foam padding to hold the pipes to the walls and floors.
• Make sure hot water pipes have room to expand so they don't knock against framing as they heat up.

3. Drain and refill the system

Older systems often have built-in air chambers that absorb sudden pressure changes, but over time they fill with water and stop working.

• Turn off the mains water supply.
• Open all taps, showers and hoses from the highest point in the house to the lowest to drain it fully.
• Once drained, turn the supply back on slowly so air can refill the chambers.

4. Fit a water hammer arrestor

If nothing else has worked, an arrestor is one of the most effective fixes.

• Pick one up from a plumbing or hardware store.
• Install it near the problem spots, like under sinks or behind the washing machine or dishwasher.
• Some screw straight onto existing fittings, while others are best fitted by a plumber.

The arrestor's shock-absorbing chamber soaks up the excess pressure and stops the banging.

5. Replace fast-closing valves

Appliances like washing machines and dishwashers have solenoid valves that close instantly, which can trigger water hammer.

• If an appliance is the culprit, add an arrestor nearby or fit slow-closing valves.
• For taps that close too fast, swap them for gradual-closing mixer taps.

When to call a plumber

If you've tried these and the banging's still there, get a professional in. A plumber can assess the system for pressure problems, faulty valves or missing air chambers, fit arrestors in the best spots for a lasting result, replace old, damaged or undersized pipes making it worse, and check for hidden leaks or weak joints that could be contributing. Water hammer can cause expensive damage over time, from leaks to burst pipes, so it's not one to ignore.

How we do it at Fix-It Right

If the hammering won't quit, we'll assess it properly and sort it for good. We keep it simple: there's $0 call-out, we give you three written quotes so you can pick what suits your budget, and you'll always know the price before we start. If the number's a stretch, Fix-It Now Pay Later gives you 12 months with no interest and no repayments. Every job is backed by our 10-year workmanship guarantee, because the whole idea is to fix it properly the first time. Plumbing fixed for good, not fixed for now.

Left unchecked, water hammer can lead to burst pipes, so it's worth sorting early. We cover Melbourne, Geelong, Ballarat and Canberra. Book online or give us a call.