A loud bang when you close a tap, or knocking when the washing machine or dishwasher fills, is usually water hammer: a pressure shock when fast-moving water is stopped suddenly. It's more than an annoying noise. Over time it can loosen fittings, damage valves and cause leaks.
Common causes
| Noise | Likely cause |
|---|---|
| Single loud bang when a tap or appliance valve shuts | Water hammer: high pressure plus quick-closing valves |
| Rattling or knocking along a pipe run | Pipes not properly clipped to the wall or roof timbers |
| Banging when hot water runs | Pipes expanding as they heat up and rubbing against brackets |
| Hammering from the geyser area | Faulty pressure control valve, or a problem with the geyser itself |
| Humming or vibrating | Very high water pressure or a worn valve |
What you can check
- Which tap or appliance causes it? Note whether it's a quarter-turn tap, a washing machine, a dishwasher or the toilet cistern refilling.
- Is the pressure very high? Taps that spray hard and taps that drip often go with it. A pressure-reducing valve may be missing or faulty. See low water pressure, which explains how home pressure is regulated.
- Look for loose pipes you can see in the roof, under basins or outside walls.
- Check the geyser overflow pipe. If it drips constantly too, the valves may need attention. See geyser overflow pipe dripping.
How a plumber fixes it
- Fit or replace a pressure-reducing valve so household pressure stays at a safe level.
- Install water hammer arrestors near quick-closing valves such as washing machine and dishwasher connections.
- Clip and secure loose pipes, and add padding where pipes rub.
- Replace faulty valves at the geyser or cistern.
Don't ignore it if
- The banging started suddenly and is getting worse.
- You also see damp patches, a rising water bill or a meter that moves with all taps off. See the hidden water leak meter test.
Compare plumbers in Benoni or geyser repair and replacement.