What is happening
Water in a pipe has weight. When a fast-closing valve shuts, like a washer or dishwasher solenoid or a single-lever faucet snapped off, the water slams to a stop. That shock wave bounces back and shakes the pipe against the framing.
Common triggers
- Washing machine finishing a fill
- Dishwasher valves cycling
- Toilet fill valve closing
- Single-handle faucets shut quickly
Water in a pipe has weight. When a fast-closing valve shuts, like a washer or dishwasher solenoid or a single-lever faucet snapped off, the water slams to a stop.
From the counter
Fixes from simple to involved
- Strap loose pipes. Pipes that bang against joists need clips. In a North York basement with an open ceiling, that may be a quick fix.
- Check household pressure. High pressure makes hammer worse. A gauge on a hose bib tells us.
- Install water hammer arrestors. Small sealed cylinders with an air cushion, fitted at the washer box or under the sink.
- Replace a noisy toilet fill valve with a quieter modern one.
Other noises that are not hammer
| Noise | Usual cause |
|---|---|
| Tick-tick-tick while hot water runs | Hot copper creeping against wood |
| Rumble from water heater | Sediment boiling at tank bottom |
| Whistle at a valve | Partly closed or worn valve |
| Gurgle in drains | Venting problem or partial clog |
Why fix it
Repeated hammer loosens joints and fittings over time and can crack soldered connections. It also shortens the life of appliance valves. A small arrestor is cheap compared with a leak inside a finished wall.
Questions
Can I install a hammer arrestor myself?
Screw-on arrestors for washer valves are easy to fit. In-line ones need cutting into the pipe.
Does water hammer cause leaks?
Over time it can loosen joints and stress fittings, especially old soldered or threaded ones.