Why Are My Pipes Knocking? Understanding Water Hammer (And Why You Shouldn't Ignore It)
- Matt Littau
- Aug 4
- 4 min read
Have you ever turned off a faucet, finished a load of laundry, or heard your dishwasher stop running—only to be followed by a loud BANG! somewhere inside your walls?
You're not imagining it, and your house isn't haunted.
That loud knocking sound is often caused by a plumbing phenomenon known as water hammer, and while it may seem like nothing more than an annoying noise, it can be a warning sign that your plumbing system is experiencing excessive pressure.
Here's what every homeowner should know.
What Is Water Hammer?
Water hammer (sometimes called hydraulic shock) occurs when moving water is forced to stop or change direction suddenly.
Water may seem soft, but when it's moving through your home's plumbing at several gallons per minute, it carries significant momentum.
When a valve closes quickly—such as when a washing machine finishes filling or a single-handle faucet is shut off—the moving water has nowhere to go.
That energy creates a pressure wave that travels back through your plumbing system at speeds approaching 4,000 feet per second, causing pipes to vibrate or slam against framing members. That's the "bang" you hear.
Why Does It Happen?
Several factors can contribute to water hammer.
Fast-Closing Valves
Modern appliances are one of the biggest culprits.
Unlike older plumbing fixtures that close gradually, today's washing machines, dishwashers, refrigerators with ice makers, and some faucets use solenoid valves that snap shut almost instantly. The quicker the valve closes, the greater the pressure spike.
High Water Pressure
If your home's water pressure is already elevated, water hammer becomes more severe.
Most residential plumbing systems operate best between 50 and 70 PSI.
When pressure consistently exceeds 80 PSI, it places unnecessary stress on pipes, fixtures, water heaters, appliance hoses, and valves—while also increasing the intensity of hydraulic shock.
Missing or Failed Water Hammer Arrestors
Many newer homes include small devices called water hammer arrestors. These contain a sealed chamber of compressed air separated from the water supply. When pressure suddenly spikes, the air cushion absorbs the shock before it travels through your plumbing.
Like any plumbing component, however, arrestors can fail over time and may eventually require replacement.
Loose Plumbing Pipes
Sometimes the pressure wave isn't the only problem.
If plumbing lines weren't properly secured when the home was built—or if mounting straps have loosened over time—the pipes themselves may physically strike wood framing inside walls or ceilings, making the noise even louder.
Is Water Hammer Dangerous?
Occasional minor water hammer isn't necessarily an emergency.
Repeated hydraulic shock, however, can gradually damage your plumbing system.
Over time, excessive pressure spikes may contribute to:
Loose pipe joints
Damaged pipe supports
Worn faucet cartridges
Leaking valves
Premature washing machine hose failure
Water heater stress
Increased wear on plumbing connections throughout your home
Think of it like repeatedly slamming a car door. Once probably isn't a problem. Thousands of times over several years? Eventually something gives.
How Can You Tell If You Have Water Hammer?
Common signs include:
Loud banging after turning off a faucet
Knocking when the washing machine fills
Pipes vibrating inside walls
Shaking near your water heater
Noise after your dishwasher finishes filling
Sudden pipe movement after using plumbing fixtures
If the sound occurs consistently after water flow stops, water hammer is a likely cause.
Can You Fix It Yourself?
Sometimes.
A few things homeowners can safely check include:
Make sure your home's water pressure isn't excessively high.
Listen for whether the sound always comes from the same fixture.
Check for visibly loose pipes in unfinished basements or utility rooms.
Pay attention to whether the problem is getting worse over time.
However, diagnosing the root cause isn't always straightforward. The noise you hear may actually originate from a completely different section of plumbing than where the pressure wave begins.
How Viking Plumbing Solves Water Hammer
Every home is different, so the solution depends on the underlying cause.
At Viking Plumbing, we begin by evaluating the entire plumbing system—not just the noisy pipe.
Depending on what we find, solutions may include:
Installing or replacing water hammer arrestors
Testing and adjusting water pressure
Installing or servicing a pressure reducing valve (PRV)
Securing loose plumbing lines
Repairing worn valves or fixtures
Evaluating washing machine and appliance connections
Inspecting your water heater and plumbing system for related issues
The goal isn't simply to make the noise disappear—it's to eliminate the excessive stress causing it.
Don't Ignore the Bang
Water hammer is one of those plumbing issues that's easy to put off because everything still seems to be working.
But unusual noises are often your plumbing system's way of telling you something isn't quite right.
Addressing the problem early can help prevent unnecessary wear, extend the life of your plumbing system, and give you peace of mind that everything behind your walls is working the way it should.
If your pipes have started banging, knocking, or vibrating, Viking Plumbing can help identify the cause and recommend the right solution before a small annoyance becomes a larger repair.
Hear a Knock Every Time You Turn Off the Water?
Don't ignore it.
Contact Viking Plumbing today to schedule a plumbing inspection. Our experienced technicians can diagnose water hammer, evaluate your home's water pressure, and help protect your plumbing system for years to come.
