Cracked Pipe? What to Do Now and How It Gets Fixed

A cracked pipe rarely stays a crack. The hairline that weeps a few drops an hour is under the same pressure every time a tap opens elsewhere in the house, and each time it opens a fraction further. Deal with it the day you find it, while it is still a drip and a tray, and it is usually a short repair on one section of pipe. Leave it and it becomes a split, and a split becomes a burst pipe.

Cracked, split or burst: which one you have

The words get used loosely, but what you are looking at decides how fast you need to move.

What you see	What it is	How urgent
A bead of water forming on the pipe, or a damp line along it, dripping now and then	A hairline crack or a weeping joint	Today. Tray under it, water off if it gets worse.
A fine spray or a steady drip that does not stop	A crack that has opened, often at a bend, a fitting or a bracket	Now. Isolate the pipe before you do anything else.
Water running freely, or the pipe visibly bulged or opened	A split or a burst	Emergency. Stopcock off, electrics near the water off, then see what to do if a pipe bursts.
Water only when a basin, bath or washing machine drains	A crack in a waste pipe, not a supply pipe	Stop using that fitting. The supply can stay on.

That last row matters more than people expect. A cracked waste pipe under a sink is not under pressure. It only leaks when water goes down it, so the answer is to stop using the sink, not to turn the whole house off.

The first ten minutes

1. Find the nearest valve. Most basins, toilets and washing machines have a small isolating valve on the feed pipe, turned with a flat screwdriver until the slot sits across the pipe. If the crack is on a pipe with no valve of its own, use the main stopcock, usually under the kitchen sink. How to turn off your water supply covers where to look in older London houses and flats.
2. Open a cold tap below the crack to drain what is left in the pipe. The drip slows and stops once the pressure is gone.
3. If it is a hot pipe, switch off the boiler or immersion heater as well. A hot water pipe carries on being fed from the cylinder after the mains is off.
4. If water has reached a ceiling, a light fitting or a socket, turn off that circuit at the consumer unit before you touch anything wet.
5. Take photos of the crack and anything the water has reached, with a ruler or a coin in shot. If this ends up as an insurance claim, the photos taken before anything was touched are the ones that matter.

Why pipes crack

The cause usually tells you whether you have one crack or the first of several, so it is worth thinking about before the repair.

Frost

Water expands as it freezes, and a pipe full of ice has nowhere for that expansion to go. The crack often appears where the pipe is coldest, in a loft, an unheated garage, an outside wall or a garden tap, and it often does not leak until the ice thaws. A pipe that cracked in the cold can sit dry for hours and then start running mid-morning. If you find a frozen pipe that has not cracked yet, thaw it slowly and check along its whole length once it is running again.

Strain at bends, brackets and fittings

Pipes move a little every time they heat up and cool down. Where a run is clipped too tightly, pulled into position during fitting, or rubbing against a joist edge, that movement concentrates in one spot, and the metal or plastic fatigues there. Cracks right beside a clip, at the heel of a bend or just behind a fitting are typical.

Over-tightened fittings on plastic

Plastic pipe and fittings do not forgive a spanner the way copper does. An over-tightened compression nut or a fitting forced onto a pipe cut out of square can crack the fitting body itself, sometimes weeks after the work was done. Our note on push-fit plumbing failures goes through the joint faults in detail.

Age and the material itself

Each material fails in its own way. Old cast iron soil stacks corrode and crack along their length, older plastic waste pipe goes brittle, and lead supply pipe splits where it has been bent or disturbed. Copper is more likely to give you a pinhole than a crack, which is a different fault with a different cause, covered in copper pipe pinhole leaks. If you are not sure what your pipework is, how each pipe material fails helps you tell them apart.

Damage

A screw or nail through a pipe during decorating, a floorboard refitted onto a pipe, or a bath panel kicked hard enough to crack the waste. These are often found months later, when the water finally shows on a ceiling below.

Where the crack is changes the job

Where	What usually happens next
Exposed copper or plastic, under a sink, in an airing cupboard, in a loft	Cut out the cracked length and join in a new piece. Usually a short job once the water is off.
Plastic waste under a basin, bath or kitchen sink	Replace the trap or the cracked length. See leaking pipe under the sink.
Soil stack or the pipe from the toilet	Replace the cracked section or the connector. Stop using the toilet in the meantime. See soil pipe leaking.
Inside a wall, in a boxed chase or under a floor	Find it first. The wet patch is often not where the crack is, because water runs along the pipe and down studs and joists before it shows.
Outside, between the boundary and the house	That is your supply pipe. A meter that keeps turning with every tap off is the usual sign.

For the hidden ones, the aim is to open the wall or floor once, in the right place, rather than chasing the damp. How to find a water leak in a wall covers what you can check yourself first, and a water meter turning with everything off is the test that tells you whether the loss is on the supply pipe outside.

Can you fix a cracked pipe yourself?

You can hold one. On a pipe you can see all the way round, a pipe repair clamp over the crack is the most dependable stopgap, and self-fusing silicone tape is the next best. Both need the water off and the pipe dry and clean before they go on, and neither is a repair. How to stop a leaking pipe temporarily shows how to fit them so they hold, and the pipes you should never patch at all.

A clamp on a crack is less reliable than a clamp on a pinhole. A crack is a line rather than a point, it tends to grow at both ends, and the stress that caused it is still there. Expect it to hold the pipe until someone arrives, not through the winter.

A cracked plastic waste trap is a different matter. It is unpressurised, the parts are standard, and plenty of people swap one themselves. The pressurised supply and heating pipes are where a DIY joint that weeps overnight costs you a ceiling.

Leave it alone if the crack is on anything connected to the boiler, on lead pipe, on a pipe you can only see one side of, or near live electrics.

How a cracked pipe is repaired properly

On accessible pipework, the cracked section is cut out with some margin either side, because the metal or plastic next to a crack has been under the same stress. A new length goes in, soldered, compression or push-fit to suit the existing run, and the pipe is re-clipped so it is no longer being pulled or rubbed. The system is then brought back up to pressure and the new joints are watched before we leave.

If the crack came from frost, the rest of that exposed run is checked and lagged, since a pipe that froze once will freeze again in the same place. If it came from strain, the clipping is corrected. Otherwise the new section cracks in the same spot next year.

For a crack you cannot see, the order is detection first, then access, then repair, then making good. We pressure test to confirm which circuit is losing water, locate it with thermal imaging, acoustic equipment or tracer gas depending on the pipe, open the smallest area we can, repair the pipe, and our own team puts back the plaster, floor or ceiling. That is our pipework repair and replacement service, and burst pipe repair if it has already let go.

Call us if

• the crack is on a supply or heating pipe and you cannot isolate it without losing water to the whole house,
• water is showing on a ceiling or wall but you cannot find the pipe it is coming from,
• your meter or boiler pressure gauge says you are losing water and nothing is visibly wet,
• or you have fitted a clamp and want it replaced with a proper repair before it lets go.

We charge £150 per hour, agreed before we attend, and if we are looking for a hidden leak and do not find it you do not pay for the time spent looking. Pricing explains how the total is worked out. Book an engineer or call the number at the top of this page, and tell us where the pipe is and what it is made of if you know. That usually tells us what to bring.