Cracked Water Pipe? What to Do and How It's Fixed

Updated July 2026 · Emergency Plumber Chelsea

Stop the water first. The main stopcock is usually under the kitchen sink, in a hall cupboard or in the cellar, and it turns clockwise to close. If the crack is on a pipe with its own isolation valve, such as the feed to a toilet, basin or washing machine, you can close that instead and keep water to the rest of the house. Our guide on how to turn off a stopcock shows which way to turn it. If the crack is on a hot pipe from a gravity-fed cylinder, closing the mains will not stop it, because the cylinder is fed from the loft tank; close the valve on the cold feed from the tank, or tie up the float in the loft tank so it stops refilling.

Drain the pipe and protect what is underneath. With the supply off, open the cold taps on the lowest floor to empty the pipework, and flush the toilets once. Put a bowl or bucket under the crack and lay towels around it. If water has reached a ceiling below, look for a bulge in the plaster and keep people out from under it. If water is near lights or sockets, switch off the affected circuit at the consumer unit. Take photos of the crack and any damage for your insurer before the repair.

A temporary repair buys time, not a permanent fix. On a dry pipe, a slip-on repair clamp with a rubber insert is the most reliable stopgap. Self-amalgamating tape, stretched tight and wound well past each side of the crack, holds a small split on a straight run. Epoxy putty works on a clean, dry pipe but will not bond to a wet or greasy surface. None of these is designed to hold mains pressure for long, and all of them fail sooner on a bend or joint. Once it is in place, turn the water back on slowly and watch the repair for a few minutes. If you are wondering whether a temporary fix can hold until morning, see how long you can leave a burst pipe.

The permanent repair is to replace the damaged length. A plumber cuts out the cracked section, usually with a little extra either side to reach sound pipe, and fits a new piece using compression, soldered or push-fit joints to suit the pipe and where it runs. On copper that is a small job when the pipe is exposed. Where the crack is inside a wall, under floorboards or in a ceiling void, most of the time goes on getting access and making good. If the pipe is old lead, it should not be patched at all, and our guide to lead pipe replacement explains the options.

Frost is the most common cause of a cracked pipe in London. Water expands by about nine per cent when it freezes, and a pipe running through an unheated cellar, loft, outbuilding or along an outside wall can split along its length on a cold night. Often you only find out when the ice thaws and water starts to escape, so after a hard frost check any exposed pipework before turning everything back on. Thaw frozen pipes gently with a hairdryer or warm cloths, never with a flame. Our guide on how to stop pipes freezing covers lagging the vulnerable runs.

Other causes are worth knowing because they affect the repair. Water hammer, the banging you hear when a tap shuts quickly, puts repeated shocks through the pipework and can crack fittings and pipes near clips and bends; our guide to water hammer and banging pipes explains how to stop it. Pipes that have been bent too tightly or fixed under strain can crack at the stress point. Nails and screws from flooring or picture hooks can pierce or split pipes hidden in walls and floors. In older Chelsea properties, some pipework is simply at the end of its life, and a crack in old galvanised or thin copper pipe can be a sign that more will follow. Our guide to burst pipe repair costs explains how the repair is usually priced.

A crack you cannot see can still be leaking. Signs of a hidden cracked pipe include a damp patch or stain on a wall or ceiling that grows over time, a musty smell, bubbling paint or lifting flooring, a drop in water pressure, the sound of running water when every tap is off, and a water meter that keeps moving with nothing in use. If you notice any of these, our guide to the signs of a hidden water leak explains how to confirm it before anything is opened up.

Heating pipes and waste pipes crack too, and they behave differently. A crack in a central heating pipe lets the system lose pressure, so a boiler that keeps needing topping up can be a sign of one; our guide to a boiler losing pressure covers this. Switch the boiler off while you wait for a repair. A cracked plastic waste or soil pipe only leaks when water is running through it, so stop using the basin, bath or toilet it serves until it is fixed. Waste leaks are easy to ignore, but they soak floors and ceilings slowly and often go unnoticed until the damage is done.

Water damage from a cracked pipe is often covered by buildings insurance as an escape of water, but the repair to the pipe itself may not be. Keep the photos, any damaged parts and the plumber's invoice, and read our guide to making an escape of water insurance claim before you contact your insurer.

If you have a cracked pipe that is leaking, or a temporary repair you do not trust overnight, call Emergency Plumber Chelsea on 020 3002 6667. Our burst pipe repair service covers cracked, split and leaking pipes across SW3, SW10, Knightsbridge, Sloane Square, South Kensington and Fulham, and for leaking joints rather than cracks see our guide on how to fix a leaking pipe joint. There is no call-out fee on jobs over 3 hours.

Quick tips

• Turn off the stopcock and open the lowest cold tap to drain the pipe.
• A slip-on repair clamp is the most reliable temporary fix on a straight run.
• Epoxy putty and repair tape only bond to a clean, dry pipe.
• After a hard frost, check exposed pipes before turning the water back on.
• Never patch a cracked lead pipe: have it replaced.

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