What causes water hammer?

What it could mean

Understand the symptoms.

A rapid change in flowing water can produce a pressure wave heard as a bang or knock.

What to do next

Make a note of the washing machine, mixer or other valve that triggers it. Avoid trial-and-error adjustments to safety valves.

When a plumber should assess it

If the fault continues, is affecting other fixtures, risks damage or cannot be identified safely, arrange a professional assessment. Similar symptoms can have different causes, so an inspection is needed before confirming a repair.

What to tell us

• Your suburb and the affected fixture or system
• Whether the problem is continuous or intermittent
• Any noises, visible leaks, odours or recent changes
• Whether it involves a single fixture or several

This article is general guidance. Do not attempt electrical, gas, pressurised, confined-space or unsafe drainage work.

Make the next conversation useful

Questions worth asking about what causes water hammer?.

• Which observations would help distinguish the likely causes?
• What can be inspected safely without disturbing concealed plumbing?
• What work, access and materials might be needed before a price can be confirmed?
• What findings would change the repair or replacement recommendation?

Make a note of the washing machine, mixer or other valve that triggers it. Avoid trial-and-error adjustments to safety valves.

For work across Sydney, check our service-area information and the booking and pricing FAQs. A written quotation should clarify the scope before work proceeds.