Banging Pipes? What Causes Water Hammer and How to Fix It

A loud bang or thud in the walls when the washing machine stops filling, the dishwasher shuts off or someone closes a faucet quickly is called water hammer. It's startling, it's annoying, and over time it's hard on your plumbing. The good news is that it's usually fixable without opening walls.

What Causes It

Water moving through a pipe has momentum. When a valve slams shut, that moving water stops suddenly and sends a pressure shock back through the pipe. The bang you hear is that shock, and sometimes the pipe itself jumping and hitting a stud.

It's most common with appliances that use fast-closing electric valves, like washing machines, dishwashers and ice makers, and with single-handle faucets that can be snapped shut.

Why It's Worth Fixing

Each shock puts stress on joints, fittings, valves and appliance hoses. Over time that can loosen connections and contribute to leaks. Water hammer is also often a sign of something else, like water pressure that's too high.

The Fixes

1. Check your water pressure. High pressure makes water hammer much worse. A $10 gauge on an outside spigot tells you where you stand. If it's above 80 psi, the pressure-reducing valve may need adjusting or replacing. See pressure-reducing valves.

2. Install water hammer arrestors. An arrestor is a small device with an air cushion sealed inside that absorbs the shock. They screw on between the supply valve and the appliance hose at the washing machine, or are installed near a problem fixture. For the washing machine, which is the most common culprit, this is often a quick fix.

3. Secure loose pipes. If a pipe is loose in its straps, it can knock against framing even with a small shock. Where pipes are reachable, in a garage, attic or under a sink, adding or tightening straps quiets them.

4. Recharge old air chambers. Some older homes have air chambers, short capped pipes near fixtures, that waterlog over time. Shutting off the main and draining the system can restore the air cushion, though arrestors are the more reliable fix.

5. Close faucets gently. A small habit, but it helps with single-handle faucets.

Other Noises That Aren't Water Hammer

• Banging or popping from the water heater while it heats is usually sediment. See water heater popping.
• Ticking or creaking as hot water runs is pipes expanding. Usually harmless.
• Humming or vibrating can mean high pressure or a failing valve.
• A toilet that refills on its own is a leaking flapper. See toilet keeps running.

Noisy Pipes?

Believe Plumbing tracks down banging pipes across Tampa Bay, from pressure problems to arrestors and loose lines. See our pipe repair services or contact us.