What Is Water Hammer?

That bang in the wall when the washing machine finishes filling is a column of moving water slamming into a suddenly closed valve: a genuine shockwave travelling back through your pipes.

Why It Matters

• It’s not just noise. Each bang is a pressure spike stressing pipes, joints and appliance hoses. Over years, hammer works fittings loose and contributes to leaks and bursts.
• It flags other problems: often excessive water pressure, loose pipe fixings, or worn tap washers fluttering under flow.
• Modern appliances make it worse: solenoid valves on washing machines and dishwashers snap shut instantly, the perfect hammer trigger.

What Causes It

• Water pressure that’s too high (the most common underlying factor)
• Fast-closing valves, such as appliance solenoids and quarter-turn taps
• Pipes inadequately clipped to the structure, free to jump and knock
• Worn jumper valves/washers vibrating under flow (more a machine-gun rattle than a single bang)

Common Mistakes or Misunderstandings

• “Old houses just do that.” It’s a fixable fault, not a character feature, and it was quieter once, before pressure crept up or clips loosened.
• “It’s harmless.” The noise is harmless; the pressure spikes causing it aren’t, especially to flexible hoses under sinks (a leading cause of indoor floods).
• “One fix suits all.” The right cure depends on the cause: a pressure limiting valve, hammer arrestors at the offending appliance, re-clipping pipes, or tap servicing.

When to Call a Plumber

Banging that started recently, gets louder, or follows a specific appliance: we diagnose the cause, check your water pressure while we’re there, and fix the source rather than muffling the symptom.