Why Do My Pipes Make a Hammering Noise?
A sudden bang or repeated hammering noise from your pipework can be alarming, especially when it happens every time you turn a tap off. This phenomenon, commonly known as water hammer, is a mechanical issue within your plumbing system rather than a sign of imminent failure, but it should not be ignored.
Left unaddressed, water hammer can loosen joints, wear out valves prematurely, and in some cases cause leaks. Understanding the likely causes helps you decide whether it is something worth booking a plumber for straight away or something that can wait until your next visit.
What Causes Water Hammer
Water hammer occurs when flowing water is suddenly stopped, usually by a closing tap or valve, and the momentum of the moving water has nowhere to go. This creates a pressure spike that travels back through the pipework, causing it to shudder or bang against joists, brackets or masonry.
The most common causes are unsecured pipework that is free to move and knock against surrounding structures, worn washers in older tap mechanisms, failed air cushions in the system, or mains water pressure that is higher than the pipework and fittings are designed to handle.
Trapped Air and Missing Air Cushions
Older plumbing systems often relied on small air pockets, sometimes called air cushions or air chambers, positioned near taps to absorb pressure spikes. Over time these can become waterlogged and lose their cushioning effect, which allows the hammering to start or return after previously being fine.
In some cases, simply draining the system and allowing air chambers to refill can resolve the issue temporarily, but if it recurs regularly, a proper mechanical fix such as a water hammer arrestor is a more permanent solution.
Loose or Unsecured Pipework
Pipes that pass through joists, walls or under floors need to be properly clipped and supported. If clips have come loose, deteriorated, or were never fitted correctly, the pipe can move slightly with every pressure change, and this movement is often what you actually hear rather than the water itself.
This is a particularly common issue in Victorian and Edwardian properties around Wimbledon and the surrounding area, where original pipework has been added to or altered many times over the decades without every section being properly restrained.
High Mains Water Pressure
If your hammering is widespread across multiple taps and appliances, it may point to excessively high incoming mains pressure. A pressure-reducing valve can be fitted to bring this down to a safer, more consistent level, protecting your pipework, appliances and fittings from unnecessary wear.
This is worth having assessed by a plumber with a pressure gauge rather than guessing, since fitting a reducing valve unnecessarily, or at the wrong setting, can create its own problems with flow rate.
When to Call a Plumber
Occasional, mild hammering that has just started is worth monitoring, but persistent or worsening noise, especially if accompanied by visible pipe movement, damp patches, or a drop in water pressure, should be looked at promptly. Our engineers can trace the pipe run, check clipping, test mains pressure, and fit an arrestor or reducing valve as needed.
Diagnostic and repair work of this kind is charged at our standard hourly rates of £99 + VAT on weekdays, £120 + VAT in the evening, and £185 + VAT overnight and on Sundays and bank holidays, with a one-hour minimum.
Need a plumber or heating engineer?
We arrange appointments across Wimbledon and south west London at clear hourly rates. Call 020 3727 2578 or request an appointment.