Water hammer (hydraulic shock) occurs when moving water abruptly stops or changes direction, sending a high-pressure shockwave through your plumbing. This creates loud banging sounds and stresses pipe joints.
The best way to fix a water hammer depends on the root cause, but the fastest and most permanent solution is installing a water hammer arrestor. These small, sealed shock absorbers cushion the impact of sudden water halts.
Water hammer is a hydraulic shock wave caused by a sudden stop in water flow. If it happens suddenly, it usually means your plumbing’s built-in shock absorbers have failed, a valve is closing too fast, or your water pressure has increased.
No, water hammer will not go away on its own. In fact, it tends to get worse over time. Ignoring the banging or clanging sounds can cause pipe joints to loosen, wear out valves, and eventually lead to burst pipes or costly leaks.
The long-term effects of water hammer might present themselves in the following ways: Leaks: Water hammer has the potential to damage joints, fittings and connections, resulting in poor seals and ultimately leaky pipes. Ruptured pipes: Ruptured pipes due to built-up pressure can be particularly expensive to repair.
You do not always need a plumber to fix a water hammer. Minor, localized hammering near appliances or fixtures can often be resolved with simple DIY fixes, such as draining your home's plumbing system or attaching in-line water hammer arrestors.
In plumbing, the "135-degree rule" is a code standard that dictates how much a horizontal drain pipe can bend or change direction. It limits the total cumulative angle of pipe fittings before a system requires an access point (cleanout) or must be vented, ensuring proper flow and preventing chronic clogs.
The best way to stop water hammer is to install a Water Hammer Arrestor near the appliances or valves causing the banging (e.g., washing machines or dishwashers). If the banging occurs house-wide, adjusting the pressure regulator to ≤60 psi and bleeding the plumbing system of trapped air are also highly effective.
The sudden, jarring sound of a water hammer itself only lasts for a brief second or two. It is caused by a shockwave that occurs when a rapidly closing valve forces moving water to stop instantly, causing it to slam against the pipe walls.
Water hammer is caused when moving water comes to a sudden stop. This creates a shockwave travelling through the plumbing system, and it's this shockwave that makes the noise. Shockwaves can be caused by a tap being quickly switched off or a valve being closed.
Water hammer isn't an immediate emergency, but it should be addressed as soon as possible. While rare, the sudden shockwaves and vibrating pressure spikes can gradually stress pipe joints, damage valves, and eventually cause burst pipes or hidden leaks over time.
Water Hammer
As you flush your toilet, the water will run quickly through the pipes, but by doing so, when the toilet finishes filling up it closes a valve which will cause all of the water to crash against it. This will be the noise and vibration you experience when flushing the toilet or starting the washing machine.
💷 Main costs to expect
Labour: Typically one to two hours, charged at around £40–£60 per hour for a qualified plumber. Materials/parts: Water hammer arrestors usually cost between £20 and £60 each depending on size and type. Extras: If pipework needs adapting or new valves fitting, this might add £30–£80.
Yes, water hammer is a common plumbing issue that affects both residential and commercial properties. The problem can occur with any plumbing fixture that requires quick shutoff, such as washing machines, dishwashers, or even standard faucets.
Left untreated, water hammer can cause significant damage by destroying pipework, the home's plumbing system, and appliances connected to the pipes. This damage has a ripple effect that can result in water damaging the home, mold issues, and structural integrity issues like rot.
Damage to Pipes: Repeated high-pressure shocks can weaken the walls of the pipes, leading to leaks, cracks, or even bursts. In severe cases, the entire pipeline could fail. Pump and Flow System Damage: Water hammer can cause significant damage to pumps, valves, and other components in the flow system.
You only need a plumber if DIY troubleshooting (like resetting the air chambers, securing loose pipes, or adjusting your water pressure) fails, if your home’s water pressure regulator is faulty, or if the banging is occurring deep inside your walls.
Probable Sources of Water Hammer
How to Stop Water Hammer
PMRs for malignancies of the stomach, kidney, brain, and lymphopoietic system were also elevated, especially among plumbers. Chronic rheumatic heart disease, emphysema, liver cirrhosis, and all external causes of death were the major non-cancer causes with significantly elevated PMRs.
Ignoring water hammer can slowly weaken and severely damage your plumbing system. Over time, the repetitive hydraulic shockwaves loosen pipe joints, wear out valves, and cause hidden leaks within your walls. In worst-case scenarios, an unaddressed pressure surge can cause a pipe to burst, leading to catastrophic property damage.
The "135 rule" in plumbing is a standard code requirement that dictates how sharply a horizontal drain pipe can bend. It states that the total aggregate bend (change in direction) in a drainage line cannot exceed 135 degrees before an access point—known as a cleanout—must be installed.
Piping systems without bends or loops: Systems that feature long lengths of pipe without directional variation can result in excessive fluid velocity, which worsens the effects of water hammer when it's inevitably caused by a closing valve.
Banging pipes at night are almost always caused by water hammer (sudden pressure shockwaves), thermal expansion (pipes expanding and rubbing against wood framing as they heat up), or trapped air. These sounds are particularly noticeable at night because the house is quiet and municipal water pressure often increases.
Yes, you can absolutely fix a water hammer yourself. The banging or thudding noise happens when moving water abruptly stops and slams against a closed valve. You can often solve this in about 30 minutes by draining trapped air, securing loose pipes, or installing shock-absorbing devices.