Cracked water pipe: what to do now and how it is repaired

What to do in the first ten minutes

Speed matters more than the repair itself. Water from a mains-pressure pipe does not stop on its own, and the damage it causes to plaster, floors and the flat below usually costs far more than fixing the pipe. Work through these steps in order and stop at any point where it is not safe to carry on.

• Turn off the water at the internal stopcock. In most London homes it is under the kitchen sink, in a downstairs cupboard or where the supply pipe comes through the floor. Turn it clockwise until it stops.
• Open the cold taps on the lowest floor to drain the pipework, and flush the toilets once.
• If the cracked pipe is on the hot side or the heating, switch off the boiler or immersion heater as well.
• If water is reaching light fittings, sockets or the consumer unit, keep clear and switch the electrics off at the consumer unit only if you can reach it from somewhere dry.
• Put a bucket under the crack, move furniture and rugs, and take photos of the pipe and any damage for your insurer.
• If you live in a flat, tell the neighbours below. Water often shows up in their ceiling before you notice it in your own home.

If the stopcock will not turn or does not stop the water, do not force it with a wrench, because old stopcocks can snap. Our guide on an internal stopcock will not shut off explains the alternatives, including the outside stop valve, and why this is the moment to call us.

Temporary fixes: what works and for how long

A temporary repair is only there to let you turn the water back on for a short time, for example to flush toilets overnight while you wait for a plumber. None of these is a permanent fix on a pipe under mains pressure, and none of them works well on a pipe that is still wet or wet through behind a wall.

Dry the pipe as well as you can before applying anything, turn the water back on slowly and watch the repair for the first few minutes. If it weeps, turn the water off again and leave it off.

Why water pipes crack

Finding the cause is part of the repair. A pipe that cracked for a reason that is still there will crack again, often a short distance along from the first repair.

Frost is the most common cause in winter. Water expands as it freezes, and a pipe in a loft, garage, outside wall or under a suspended floor can split along its length. The crack often only starts leaking once the ice thaws, which is why a burst frequently appears on the first milder day after a cold snap. Our guide to frozen water pipes covers what to do while the pipe is still frozen.

• Freezing in unheated spaces or on pipes close to an outside wall.
• Corrosion in old copper, which shows up as green crusting, pinholes and weeping joints, often on pipework several decades old.
• Physical damage, such as a nail through a floorboard or a screw into a wall. If you have drilled through a water pipe, that guide explains the extra checks needed.
• Movement and vibration, for example pipes that are not clipped properly or pipes that bang when a tap closes.
• Ageing plastic, fittings stressed during installation, or a push-fit joint that was not pushed fully home.
• Ground movement or heavy traffic over an underground supply pipe.

Is it a cracked pipe or something else?

Not every wet pipe is cracked. Water dripping from a cold pipe in a warm, humid room may simply be condensation, and a leak can run along a pipe for some distance before it drips, so the wet spot is not always where the fault is. Wipe the pipe dry, then watch where water first reappears.

Cracks you cannot see are usually found through their effects: a damp patch or brown stain on a ceiling, bubbling paint, a musty smell, a floor that feels soft, lower water pressure, or the sound of water running when every tap is closed. A water meter moving with taps off is one of the most reliable signs of a hidden leak on the supply side. If you have ceiling leaking water now, deal with that first and then trace the source.

How a cracked pipe is repaired properly

A plumber will first isolate the section, drain it and cut out the damaged length with some margin either side, because the pipe next to a frost split or corrosion hole is often weakened too. New pipe is then joined in using compression, soldered or push-fit fittings depending on the pipe material, the location and whether the joint will be hidden. Joints that will be boxed in or buried need extra care, because they will be hard to reach later.

Where the crack is behind a wall or under a floor, the work includes opening up enough to reach the pipe safely, and afterwards the section is pressure-tested before anything is closed. If the pipework is corroded along its length, patching one crack after another is poor value, and replacing the run is often the better decision. Our burst pipe repair and pipework installation services cover both.

If the leak is somewhere you cannot find, or it is on the underground supply pipe between the boundary and the house, it becomes a leak detection and repair job rather than a simple pipe repair. Responsibility for that supply pipe usually sits with the homeowner, which our guide on water supply pipe responsibility explains.

After the repair: drying out and insurance

Once the pipe is fixed, the building still needs to dry. Ceilings that have taken a lot of water can hold it for some time, and replastering or redecorating too early traps moisture. Drying a home after a plumbing leak covers what normally happens before repairs to finishes.

Many home insurance policies cover the damage caused by escaping water, and some include trace and access insurance cover for finding a hidden leak. The pipe repair itself may or may not be covered, so check your policy wording. Keep your photos, the plumber's description of what failed and why, and any invoice. If frost caused the crack, pipe insulation for unheated spaces is the cheapest way to stop it happening again next winter.

When to call a plumber

Call straight away if water is coming through a ceiling, if you cannot turn the water off, if the crack is on a hot water or heating pipe, or if you have no water at all while the supply is isolated. Call too if the pipe is hidden, if a temporary repair is weeping, or if this is not the first crack on the same run.

Loyal Plumbers runs 10 vans across London and everywhere inside the M25, 24 hours a day. When you call, tell us where the pipe is, whether you have managed to turn the water off and whether any water has reached electrics or another flat. Our call-out charge is £60, and the engineer explains what the repair involves before any work starts.