What water hammer is
Water moving through a pipe carries momentum. When a valve shuts quickly, such as a washing machine solenoid or a single-lever faucet snapped closed, that moving water stops abruptly and sends a pressure shock back through the line. You hear it as a bang or a thud in the wall.
Higher incoming pressure makes the shock stronger. Pipes that are not well secured to framing make it louder, because they move and strike wood or each other. Over time, repeated shocks can loosen fittings and wear on valves and appliance connections.
Sounds and what they usually mean
| What you hear | When | Likely cause |
|---|---|---|
| Single loud bang | Right after a valve closes | Water hammer, often made worse by high pressure |
| Rapid chattering or machine-gun noise | While a toilet refills or a faucet runs | Worn fill valve or faucet part vibrating |
| Ticking in walls | As hot water starts or stops | Pipes expanding and contracting against framing |
| Whistling or squealing | While water runs | Restriction in a valve or regulator |
How a plumber usually approaches it
- Measure static pressure.A gauge on an outdoor hose bib shows pressure with no water running. The reading is compared with the plumbing code's maximum for homes.
- Inspect the pressure regulator.If the house has one, it is checked for age, setting and whether pressure creeps up over time.
- Find the source fixture.Washing machines, dishwashers and quick-closing valves are common triggers.
- Choose the fix.Adjusting or replacing the regulator, adding water hammer arrestors near the triggering appliance, and securing loose pipe where it can be reached.
Parts you may hear about
- Pressure regulator (PRV)
- A bell-shaped valve on the main line that reduces incoming pressure to a set level for the house.
- Water hammer arrestor
- A small device with a sealed cushion that absorbs shock waves near a quick-closing valve.
- Expansion tank
- A tank near the water heater that absorbs water expansion when the system is closed by a regulator or check valve.
- Static pressure
- Pressure measured with no water flowing anywhere in the house.
Questions to ask
- What is my static pressure, and is it within the code limit for homes?
- Is my regulator adjustable, and how old is it?
- Which appliance or fixture is causing the hammer?
- Would arrestors at that appliance solve it, or is pressure the main issue?
- Do I need an expansion tank after this work?
Common questions
Is water hammer dangerous?
It is not usually an emergency, but repeated pressure shocks add stress to pipes, fittings, appliance hoses and valves. It is worth addressing, especially if pressure is high.
Where is my pressure regulator?
When a home has one, it is often near where the main line enters the house, sometimes near the front hose bib. Not every home has one.
Can high pressure damage my water heater?
High pressure can make the relief valve discharge and adds stress to the tank and connections. Measuring pressure is a good first step when a relief valve drips.
General information for Golden Hills, not a quote or professional advice. In an emergency, call 911.