What causes water hammer in my pipes and how do I fix it?

Water hammer happens when fast-moving water inside a pipe stops abruptly, creating a shock wave that makes a loud banging sound. It’s not just annoying—over time, it can damage fittings or even cause pipes to burst. Here’s how to identify the problem and what you can do to fix it.

TL;DR

• Water hammer is caused by sudden changes in water flow that create pressure shock waves.
• A waterlogged air chamber is the most common cause when the noise begins suddenly.
• Draining your plumbing system often restores the air cushion and stops the banging.
• If no air chambers exist, install hammer arrestors or correct high water pressure.
• Chronic banging or pipe damage may require help from a professional plumber.

What is water hammer?

Water hammer is a specific kind of plumbing noise—not just general pipe clatter. It occurs when flowing water is shut off quickly, creating a pressure surge that “hammers” the pipe. Properly installed plumbing includes air chambers that cushion this impact, but over time those chambers can become waterlogged and lose effectiveness.

Why water hammer suddenly starts

If you never had water hammer before and it suddenly begins, your air chambers may be full of water. To fix this, turn off the water behind the affected section and open the faucet to let the water drain completely. When the chamber empties, air will refill it and restore the cushion.

If the air chamber is below the outlet, you may need to drain the main supply lines. Chambers can also clog with mineral residue; in that case, removing the cap and cleaning out debris usually restores function.

What if your plumbing has no air chambers?

Some homes were built without air chambers entirely. Because water hammer can eventually damage pipes or fittings, it’s important to address the problem. Start by checking whether you can reduce the water pressure. If lowering pressure isn’t feasible, a professional Boston plumber can install a pressure-reducing valve or add hammer arrestors that fit into tight spaces.

When to call a plumber

If you continue to hear banging or clattering after trying these steps, or if you suspect leaking, sweating, or frozen pipes, schedule plumbing service promptly. Fixing the issue early helps prevent more serious damage.