Pipes Bang When Water Is Turned Off
A loud bang when a faucet or valve shuts off is commonly called water hammer. It's a shock wave that travels through the pipe when flowing water is suddenly stopped. Banging pipes can have several possible causes — not just one — including water hammer from fast-closing valves, excessive water pressure, loose or inadequately supported piping, appliance solenoid valves, pressure-regulating valve issues, or thermal expansion in closed systems. A plumber checks each of these rather than assuming a single cause, because the right fix depends on which factor (or combination of factors) is actually at play.
- —Water hammer from fast-closing valves (washing machines, dishwashers, ice makers) creating a shock wave when flow stops suddenly
- —Excessive water pressure (above 80 psi) making the shock wave more violent and more likely to cause noise
- —Loose or inadequately supported piping that rattles against framing when water flow changes
- —Missing or failed water hammer arrestor (a small air chamber that absorbs the shock) where fast-closing valves are present
- —Pressure-regulating valve (PRV) issues — a failed or misadjusted PRV can allow pressure to rise high enough to worsen hammering
- —Thermal expansion in a closed system (no expansion tank) causing pressure spikes when the water heater heats
Try This First
Safe, simple steps you can try yourself. If any step feels beyond your comfort level, skip it and continue below.
- 1
Test the pressure
Check pressure at an outdoor spigot with a gauge. If it's above 60 psi, high pressure may be contributing to the banging. A PRV adjustment or replacement may be needed.
- 2
Try recharging air chambers
Turn off the main water supply. Open the highest faucet in the house and the lowest (or a hose bibb). Let the system drain completely for 15 minutes. Turn the main back on. This refills old-style air chambers with air, which can absorb the shock.
- 3
Identify which fixtures cause it
Does it happen when the washing machine shuts off? A toilet finishes filling? A dishwasher valve closes? Fast-closing solenoid valves are a common trigger.
- 4
Check for an expansion tank
If you have a closed system (a PRV or backflow preventer with no bypass), thermal expansion from the water heater can cause pressure spikes. An expansion tank may be needed.
If the problem is resolved
If draining and recharging the system stops the banging, old-style air chambers were waterlogged. This fix may need to be repeated every year or two. If lowering pressure or adding an expansion tank resolved it, that was the contributing factor.
If the problem persists
If the banging persists after recharging, the cause may be loose pipes, missing arrestors, high pressure, or a combination of factors. A plumber can check each possibility. Continue below.
Stop and Call a Plumber If…
- The banging is loud and violent — it can damage pipe joints over time
- Pressure reads above 80 psi (high pressure worsens water hammer)
- You see a leak at a pipe joint after the banging
- The banging started suddenly after years of quiet operation
- ✓Testing water pressure with a gauge to determine if excessive pressure is a factor
- ✓Checking for and installing water hammer arrestors at washing machine boxes and other fast-closing valves
- ✓Securing loose pipes with proper hangers and straps
- ✓Testing and adjusting the PRV if pressure is above 60 psi
- ✓Checking for thermal expansion and whether an expansion tank is needed on a closed system
- ✓Checking for damage at pipe joints and fittings
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Ask the AI PlumberReviewed by Paul Hall, Owner & Licensed Plumber
The Classic Plumber · Knoxville, TN · License #4268. This guidance is general — an onsite inspection may be required for a confirmed diagnosis.