Right after you turn off a faucet, you might hear a sharp thump or bang behind the wall. That noise, known as water hammer, happens when pressure builds suddenly inside your pipes. It’s not just a strange sound. If it keeps happening, it can lead to much bigger plumbing problems. Once you understand where the sound comes from, you’re already halfway to a fix.
What That Loud Banging Sound Really Means
Water moves through your pipes quickly, especially when you use home appliances like dishwashers or washing machines. When that flow stops too fast, the momentum has nowhere to go. That pressure hits a valve or a bend in the pipe, and the force sends a shockwave through the system. Pipes can rattle against walls, floors, or wood framing. That thud you hear is the result of that shock pushing the pipe to its limit.
What Causes Water Hammer in the First Place
The issue usually starts when a valve closes fast. That can happen with older faucets, automatic washing machine valves, dishwashers, or even certain showerheads. When the valve closes, the moving water suddenly hits a wall. It has nowhere to go, so it surges back through the pipe and creates vibration. That vibration shakes the line, especially in homes where pipes aren’t fully secured to framing. Sometimes, the problem gets worse with time. Older homes might have had devices called air chambers — basically vertical pipe sections filled with air — that were designed to absorb some of that shock. But air doesn’t stay put forever. With use, water can fill those chambers, and when that happens, the pressure wave hits hard without anything to slow it down. Newer homes often use water hammer arrestors instead, but even those can wear out or stop working if sediment builds up inside the system. Here in Northern Minnesota, where we have hard water, limescale buildup is a common problem. It increases the chance of water hammers and can interfere with arrestor devices by restricting flow.
Why It’s More Than Just a Noise Problem
It’s tempting to ignore water hammer, especially if it doesn’t happen all the time. You turn off the faucet, hear the bang, and go on with your day. But each time it happens, the system takes a hit. Pipes that rattle eventually loosen from their supports. Valves wear out faster. Soldered joints and fittings can develop tiny leaks. And those small leaks can lead to wall damage, mold, or wasted water without much warning. The shockwave also travels backward toward the main line. If you’ve got older pipes or aging valves, that backflow of energy adds stress to parts that might already be close to failing. It’s not unusual for water hammer to go hand in hand with pressure spikes, valve noise, or inconsistent water flow. Ignoring it long enough means you might be looking at more than just a fix for noise — you might need to deal with leaks or pipe damage that could have been avoided.
Can Water Hammer Damage Appliances?
Any appliance that connects to your water line can feel the effects of water hammer. That includes your dishwasher, washing machine, refrigerators with water dispensers, water heaters, and even some newer coffee machines. These appliances rely on built-in valves to control water intake. When pressure surges hit those valves repeatedly, the internal parts wear out. That leads to leaks, failed components, and repair calls that come sooner than you expected. Some manufacturers include warnings about pressure shock in their manuals. That’s because this isn’t a rare problem — it’s just one that many homeowners don’t realize is linked to the sounds they’re hearing. The fix doesn’t come from replacing the appliance. It comes from treating the plumbing system as a whole. If you’ve replaced a washer valve more than once or had issues with appliance leaks shortly after installation, water hammer might be part of the reason.
When You Should Call a Professional
You might feel comfortable checking your water pressure, especially if you already have a pressure gauge on hand. If the pressure reads over 80 psi, that’s higher than most homes need. You can lower it using a pressure-reducing valve, if you have one installed. Dropping it into a better range — between 50 and 70 psi — may reduce the impact of water hammer, or even stop it completely in minor cases. That said, most long-term fixes need more than a pressure adjustment. A licensed plumber can trace where the shock is coming from and figure out which valve, appliance, or section of piping is creating the problem. That might mean checking the washing machine hookups, adding arrestors, inspecting your water heater, or replacing an old valve that shuts too quickly. In some homes, the solution is as simple as draining and refilling the system to restore air to the old chambers. In others, the fix involves installing dedicated hammer arrestors to protect individual lines.
What Are Water Hammer Arrestors?
A water hammer arrestor is a small device that absorbs pressure inside your plumbing system. It usually looks like a short stubby cylinder and gets installed near the valve or appliance that’s creating the problem. Inside the arrestor, there’s either a piston or an air bladder that cushions the shock wave and prevents it from slamming against the pipe. These devices come in different styles, including threaded models for appliance hookups and larger fittings for main supply lines. A plumber chooses the right size and location based on where the noise is happening and how your system is laid out. The goal is to stop the shock as close to the source as possible. That way, the vibration doesn’t have a chance to echo through the rest of your home. Once installed, arrestors usually work without any maintenance.
Securing Loose Pipes to Prevent Rattling
Sometimes, the loudest part of water hammer doesn’t come from the pressure — it comes from pipes that aren’t properly secured. When pipes move, even a small shock can sound like something much worse. You might hear loud bangs in the middle of the night when no water is running, or feel vibrations through the floor or walls. That movement makes the problem worse by wearing out joints and causing stress in areas that weren’t built to flex. A plumber can anchor those loose pipes with brackets, clamps, or padded straps. This work often happens behind walls, in crawl spaces, or under floorboards where the movement isn’t visible. In finished basements or tight mechanical rooms, the fix might involve adding foam insulation or adjusting how the pipe runs through a joist. The key is to keep the pipe from bouncing or shifting when the pressure wave hits. Once the movement stops, the sound usually goes with it.
What You Can Do in the Meantime
While you’re waiting for a plumber to take a look, there are a few small steps you can take to reduce the impact. Turn off appliances slowly if possible. That includes washing machine valves or older-style faucets that snap shut. Lowering your water pressure, if you’re comfortable with it, may also soften the shock. You can test this with a simple pressure gauge at an outdoor spigot or laundry hookup. If you hear banging from a specific fixture, like a shower or toilet, try listening closely to when it happens. That information helps the plumber narrow down the location of the problem faster. It’s also helpful to make a note of when the noise started, how often it happens, and whether it’s gotten worse. These details can make a big difference when diagnosing the issue and figuring out the best repair option.
Stop Your Water Hammer Today
Water hammer might seem harmless at first, but it’s often a sign your plumbing needs attention. Our team at Benjamin Franklin Plumbing® is here for you to help with silencing the noise and protecting your plumbing. If it’s too late and something breaks, we’re here to help with emergency plumbing, repiping, water heater, sewer, and other plumbing services for homeowners in Northern MN. Call us today.
