You turn off a faucet and hear a loud bang from inside the wall. Or the washing machine finishes filling and there's a hard thud that shakes the pipes. That's water hammer — and while it might sound like just an annoying noise, it's a sign of pressure problems that can damage your plumbing over time.
What Causes It
Water is heavy, and when it's moving through your pipes at full speed and suddenly has nowhere to go — because a valve snapped shut — all that momentum slams into the closed valve and the pipe walls. The result is a pressure spike that can be several times higher than your normal water pressure, and the bang you hear is the pipe physically jerking from the force.
The usual triggers:
- Washing machines and dishwashers. Their solenoid valves close almost instantly, which is why water hammer often shows up when these appliances run.
- Quick-closing faucets. Single-lever faucets shut off much faster than old twist handles, so they're more likely to cause hammer.
- Toilet fill valves. A worn fill valve that slams shut can hammer every time the tank refills.
- High water pressure. If your home's pressure is already above 80 PSI, every valve closure hits harder. Most homes should sit between 40 and 60 PSI.
Why You Shouldn't Ignore It
An occasional soft knock isn't an emergency. But repeated, hard water hammer does real damage over time:
- Loosened pipe joints and fittings. Every shock loosens things a little more. Eventually something gives.
- Cracked pipes. The pressure spikes stress the pipe walls, especially at elbows and joints.
- Damaged appliances. Your washing machine, dishwasher, and water heater all take a beating from repeated pressure spikes.
- Leaks inside walls. The worst outcome — a joint fails where you can't see it, and you find out when the drywall starts bubbling.
What Fixes It
Water hammer arrestors. These are the real fix. They're small sealed chambers with a cushion of air (or a spring-loaded piston) that absorb the pressure spike when a valve closes. They install on the supply lines near the offending fixture — behind the washing machine, under the sink, at the dishwasher connection. Inexpensive parts, straightforward install, and they actually solve the problem.
Check your water pressure. If it's running high, a pressure-reducing valve (PRV) on your main line brings the whole house down to a safe range. This alone can eliminate hammer in many homes, and it extends the life of every fixture and appliance you own.
Secure loose pipes. Sometimes the banging is made worse by pipes that aren't properly strapped. If you can access the run — in a basement ceiling, for example — adding pipe straps or cushioning where the pipe contacts framing cuts the noise and the movement.
Drain the system (temporary). Older homes sometimes have air chambers — vertical dead-end pipe stubs meant to cushion hammer — that fill with water over time and stop working. Shutting off the main and draining the system can restore the air cushion temporarily. But air chambers are a dated solution; arrestors are the permanent fix.
When to Call a Plumber
If the hammer is loud, happens with multiple fixtures, or started suddenly, get it checked. Sudden onset can mean a failed PRV or a pressure spike from the municipal supply, and that's worth diagnosing properly. And if you're hearing banging you've never heard before after a plumbing repair or appliance install, something in the new work is likely the trigger.
That banging isn't just noise — it's your plumbing telling you something's wrong. Call Concepts Plumbing at (705) 715-1513 for a free estimate in Barrie and Simcoe County. We'll track down the cause and put a stop to it before it turns into a leak.
