Water Hammer: Why Your Pipes Bang and How to Stop It

You turn off a faucet, or the washing machine finishes filling, and somewhere in the wall there is a loud thud. That is water hammer. Water moving through a pipe has momentum, and when a valve stops it suddenly, that energy has nowhere to go. It sends a pressure spike back through the line that rattles and bangs the pipe. The noise is the warning. The real concern is what those spikes do to joints, valves, and appliance connections over years.

Common causes

• •Quick-closing valves. Washing machines, dishwashers, ice makers, and some single-handle faucets shut off almost instantly.
• •High water pressure. The higher the pressure, the more violent the stop. Some neighborhoods see pressure well above what household plumbing needs.
• •Loose pipe straps. Pipes that are not secured to framing can swing and strike studs when a pressure wave passes.
• •Waterlogged air chambers. Older homes sometimes have capped vertical pipes meant to cushion shocks, but they fill with water over time and stop working.

Step one: check your water pressure

A pressure gauge that threads onto an outdoor hose bib costs very little at a hardware store and gives you a direct reading. Turn off all water inside and read the gauge. If it reads above 80 psi, a pressure reducing valve (PRV) is the first fix. If you already have a PRV and the pressure is still high, the valve may be failing. They typically wear out after 10 to 15 years. Lowering the pressure quiets water hammer, protects appliances, and reduces water waste.

Install water hammer arrestors

A water hammer arrestor is a small device with a sealed air cushion and piston that absorbs the pressure spike. They install at the problem fixture, most often on the hot and cold valves behind the washing machine, or under a sink feeding a dishwasher. Unlike old air chambers, modern arrestors do not waterlog, so the fix lasts.

Secure loose pipes

If the banging happens in a spot you can reach, like an attic, garage, or crawl space, look for pipes that move when you push them. Adding straps or cushioned clamps can stop the noise immediately. In many Central Florida homes built on slabs, supply lines run through the attic, which makes them easier to check.

Recharging old air chambers

If your home has air chambers, you can sometimes restore them by shutting off the main water, opening the highest and lowest faucets to drain the system, then closing them and turning the main back on. This refills the chambers with air. If the banging comes back within weeks, arrestors are the better long-term answer.

• Residential plumbing repairs
• Low water pressure causes and fixes
• How to find your main water shutoff