What Is That Banging in My Pipes?

That single loud bang, or a rapid shudder, when a tap closes or the washing machine finishes filling is called water hammer. It is not a ghost in the walls, it is physics. Water moving through your pipes has momentum, like traffic on a freeway. When a valve slams shut, the moving column of water has nowhere to go and stops almost instantly. The energy has to go somewhere, so it becomes a pressure spike that hammers through the pipework and shakes it against whatever it is touching.

The noise you hear is usually the pipe itself jumping and striking a stud, joist or wall lining. The pressure spike behind it can be several times your normal mains pressure, which is why water hammer is worth fixing rather than just living with. Each bang stresses joints, flexes copper, and works fittings loose a little more.

Two things have to combine to make the classic bang: something closing the water off quickly, and pipework that is free to move.

The fast closers in a modern home are usually solenoid valves inside washing machines and dishwashers, which snap shut electrically in a fraction of a second. Quarter-turn ceramic disc taps and mixers are the other common trigger, because a flick of the wrist stops full flow instantly, where an old-style washer tap took several turns to wind down. This is why plenty of Brighton homes never banged until a renovation swapped the old tapware for mixers, or a new dishwasher went in.

The movement side comes from pipe fixing. Pipes should be clipped to the frame at regular intervals. In older weatherboard homes around Hampton and Brighton East, decades of subfloor work often leave long unclipped runs of copper under the floor, and original clips rust or fall away. A well-secured pipe can absorb a pressure spike with a dull thud you never notice. An unsecured one slaps the frame and telegraphs the noise through the whole house.

The right fix depends on the cause, which is why we start by working out exactly which fixture triggers the bang. Turning appliances and taps on and off one at a time while someone listens usually narrows it down quickly.

Most water hammer is a nuisance rather than an emergency, but there are versions of it that deserve prompt attention. A bang that has recently become much louder can mean a clip has failed and a pipe is now moving freely. Repeated hammering in older galvanised or thin-walled copper pipework, common in pre-war Brighton homes, can eventually open a pinhole leak or split a joint, and the first sign is often a damp patch on a ceiling or wall.

A different noise worth knowing about is a rapid machine-gun rattle when a toilet cistern is filling, or a groan when a tap is partly open. That is usually a worn valve washer or float valve vibrating rather than true water hammer, and it means the valve is on the way out. Constant humming or banging with no fixture in use at all can indicate a failing pressure valve or, occasionally, a problem on the street main, which is your water corporation’s side to investigate.

In Victoria, fitting arrestors, pressure limiting valves or new isolation taps is licensed plumbing work. The homeowner-safe steps are the diagnostic ones: note which fixture triggers the noise, check whether any visible pipes under the house move when it happens, and tell us what you found. With that information we can usually quote the fix accurately before we arrive, and confirm it with a fixed price before any work starts.