Burst pipe repair

The first five minutes

What you do in the first few minutes decides how much of the damage you are paying to put right afterwards. A 15mm pipe at mains pressure puts out a remarkable amount of water in a very short time, and almost all of the cost of a burst is what the water does to the building, not what the plumber does to the pipe. The order of the first moves is the same for any water escaping in the house, whether the source is a split pipe, a failed connector or a cylinder, because stopping the flow always comes before finding out what broke.

Close the main stopcock. It is a small brass valve on the incoming cold main, and in most London properties it sits under the kitchen sink, in a cupboard near the front door, or under the stairs. In a purpose built flat it is often in a communal riser cupboard on the landing rather than inside your own front door. If it is stiff, and old stopcocks usually are, use both hands and turn slowly rather than forcing it with a spanner, because snapping the spindle off leaves you with no way to stop the water at all.

Now open the taps. Every cold tap, and the bath, and flush the toilets once. That empties the pipework above the burst into the drains instead of into the ceiling. Leave them open until the flow dies to nothing. If the leak is on a hot pipe, switch off the boiler or the immersion heater and open the hot taps too.

Deal with the electrics before you deal with the water on the floor. Water tracking through a ceiling finds the downlights and the cable runs first, because that is where the holes are. If any part of a wet area has a light, a socket, a shower pull cord or a fitting in it, switch that circuit off at the consumer unit, or the main switch if you are not sure which one it is. Do not stand in water to reach the board, and do not put a bucket under a light fitting and leave it there with the power on.

If the water will not stop after the stopcock is closed, it is not coming from your cold main. That usually means it is a stored feed draining down, a hot water cylinder leaking under its own stored pressure, or that the water is not yours at all and is coming from the flat above. A leaking cylinder has its own set of first checks, because the tundish, the relief valves and the cylinder connections each fail in a different way. Say which it looks like when you call, because it changes what the engineer brings and where they start.

• Close the main stopcock, clockwise, both hands, no spanner
• Open every cold tap and the bath to drain the system down
• Switch off the boiler or immersion heater if the leak is on hot pipework
• Isolate the electrical circuit for any wet area at the consumer unit
• Move what you can out of the way, and photograph the damage before you mop

Never touch a light fitting, socket or switch that is wet or has water running near it, and do not use the shower or the cooker to test whether the water has gone. Isolate first, look second. If you want that order on one page while it is happening, our short guide to what to do first when water is escaping covers it.

Find your stopcock now, not during the flood

The single most useful thing you can do about a future burst is to find your stopcock this week and turn it off and on once. If the honest answer to where is my stopcock is that you have never looked, a dry afternoon is a far better time to find out than a wet midnight. Most people discover where it is while standing in water in the dark, and a surprising number discover that it has seized solid and will not turn at all, or that it turns and the water keeps running because the washer inside has perished.

A stopcock that has not been operated in twenty years is a stopcock you cannot rely on. Exercising it once or twice a year keeps it free. If it will not shut off cleanly, replacing it is a short job and it is worth doing before you need it rather than after. In a flat, check whether your isolation is inside your own property or out on the landing, and whether you can actually get into that cupboard without a key from the managing agent.

It is also worth knowing where the isolating valves are on individual appliances. Most modern installations have a small service valve on the feed to each basin, toilet, washing machine and dishwasher, turned with a screwdriver slot. If the burst is on a flexible tap connector under a basin, closing that one valve stops the water without shutting off the whole property.

What actually makes a pipe burst

Bursts are not random. There are a handful of mechanisms and the London housing stock leans heavily on two or three of them.

Freezing is the classic one and it does most of its damage in the places nobody heats. Water expands as it turns to ice, and the ice plug itself does not usually split the pipe at the point where it forms. Pressure builds between the ice plug and the nearest closed tap, and the pipe fails at its weakest point somewhere along that trapped section, often at a soldered joint. That is why the loft, the garage, the outside tap and the pipework in an unheated void are the usual casualties, and why the burst frequently only reveals itself when everything thaws and the water starts to move again.

Corrosion is the slow one. Copper in contact with wet screed, plaster or certain insulation materials pits from the outside in, and eventually a pinhole opens up. Old galvanised steel pipe, still present in plenty of older London properties, rusts from the inside and loses wall thickness until it splits. Neither of these gives much warning beyond a damp patch that comes and goes.

Mechanical damage accounts for a lot of the calls that come in during building work. A screw or a nail through a floorboard into the pipe underneath is extremely common, and it often does not leak properly for weeks because the fixing itself is plugging the hole. Pull the carpet up or move a unit six months later and the water arrives all at once.

Then there is pressure and age. London mains pressure varies by area and can be high, and a pipe run that was fine for decades will find its weak point when pressure spikes, or when a joint that hard water scale has been quietly sealing gets disturbed by unrelated work nearby. Hard water is a real factor here, and what London hard water does inside a pipe is the same thing it does inside a hot water cylinder. Scale builds inside the bore, narrows the pipe, increases velocity and puts more stress on elbows and joints, and it also has a habit of holding a failing compression joint together right up until somebody moves it.

• Freezing in lofts, garages, outbuildings and unheated voids, splitting at a joint
• External corrosion of copper buried in screed or damp plaster
• Internal corrosion of old galvanised steel pipework
• Screws and nails through floorboards during flooring or carpet work
• Failed compression joints and perished flexible tap connectors
• Plastic push fit fittings that were never fully inserted when installed

How the burst is found when the water is not obvious

Sometimes the pipe has split in plain sight and the job is simply to cut it out and replace it. More often the water appears on a ceiling two rooms away from the fault, because water runs along the top of a joist, sits in screed and tracks down the inside of a party wall before it finds a way through. Cutting into the stain is how people end up opening half a floor and finding dry pipe under all of it.

The first question is which system is losing water. Close the stopcock and watch the water meter or the leak indicator if there is one. If it stops, the loss is on the incoming cold main. If water keeps coming, the engineer works through the stored and heated sides, isolating and pressure testing section by section so the loss shows on a gauge rather than on your ceiling. A circuit that holds pressure for a sustained period can be ruled out and left alone.

Where the pipe is buried, this becomes leak detection and repair work, and the equipment narrows the fault down before anything is opened. Acoustic listening picks up the hiss of pressurised water escaping through a small hole, and it is strongest on mains and pressurised feeds. Thermal imaging maps the warm bloom where a hot or heating leak is pooling under a floor, and is just as useful for showing where not to cut. Tracer gas resolves the silent ones, the slow weep in buried plastic pipe that makes no useful noise and carries no heat, by putting a hydrogen and nitrogen mix into the drained pipe and picking it up at the surface as it rises through the screed.

Not every damp patch is a burst pipe. Perished sealant around a shower tray, a cracked waste under a bath, condensation dripping off cold pipework in an unventilated cupboard, and rain tracking in at a parapet or a roof abutment all present as a stain on a ceiling. A good engineer will tell you when the water is not plumbing rather than open a floor to prove a point.

How a burst pipe is actually repaired

The repair itself is usually the quickest part of the visit. The section is isolated and drained, the pipe is cut back to sound material either side of the failure, and a new piece is jointed in. On copper that means either soldered fittings or compression, depending on whether the pipe can be got properly dry and whether there is a fire risk in the void. On plastic barrier pipe it means the correct fitting for that particular pipe system, with the insert in place, because pipe systems are not interchangeable and a fitting from the wrong family is a future leak.

A split caused by freezing is cut out generously rather than trimmed tightly, because the ice usually stressed more of the pipe than the visible split suggests. If a joint has failed, the engineer looks at why: a compression joint that has weeped because it was never properly tightened is remade, but a joint that failed because the pipe behind it is corroding needs more than a new olive.

Repair clamps and self amalgamating tape have a place, and that place is holding water back for a few hours until a proper repair can be made, usually because the pipework is under a floor somebody cannot open until the morning. They are not a repair. Anybody who leaves a clamp on a pressurised pipe and calls the job finished has sold you a leak with a delay on it.

Where the burst is on buried pipework and opening the floor is the expensive part, rerouting is often better value than repairing in place. Copper that has pinholed once under a solid floor tends to pinhole again somewhere else on the same run, and running a new leg through an accessible route saves opening the same floor twice. We will say so when that is the case rather than repair a single hole and let you find out in six months. Outside the building the answer is different again: a failed main under a drive or a garden is usually replaced by no dig methods, pulled through on the same route from a small pit at each end, so the surface is never opened. That no dig pipe repair approach is worth asking about before anyone quotes for a trench, because the reinstatement of a drive or a patio is usually the largest line on the job.

The rate is fixed before we attend and the total depends on how long the job takes. Access and drying time are the variables on a burst, not the repair itself.

Bursts in flats and on shared pipework

In a converted or purpose built flat the water you can see is frequently not from your own pipework. A burst two floors up will travel down a riser, along a joist and appear through your ceiling, and by the time it reaches you there is nothing in your property to fix. An engineer can establish, from your side, whether the water is entering from above, from your own pipes, or from the structure itself, and that answer is what you take to your neighbour or the managing agent.

We cannot work on pipework inside another property without the occupier there and agreeing to it, and we cannot cut into communal risers or shared services without the freeholder or the managing agent authorising it. That is not caution for its own sake. Communal pipework serves other homes and isolating it affects them.

Victorian conversions are their own category. Pipework in them has usually been added to by several different people over several decades, often with no record of where anything runs, and the original lead or steel work sometimes survives in odd corners. Boxed in runs, pipes chased into walls without protection, and feeds that pass through a neighbouring flat are all normal findings rather than surprises.

Drying out and making the damage good

Once the pipe is repaired, the building still has water in it, and that is the part that takes the time. Plasterboard, joists, screed, floor voids and insulation all hold water, and sealing a wet structure back up traps the moisture where it turns into mould, lifts flooring and blows plaster months later. A void that is genuinely wet has to dry before it is closed permanently.

Access is kept to the smallest opening that allows an engineer to work: one board lifted rather than a run of them, screed cut to the size of the joint, a tile removed whole where it can be. You get told what is coming before it happens, and where a pipe runs under a kitchen unit or a staircase, the choice between opening from above or approaching from the ceiling below is yours once you understand what each one costs you.

Reinstatement means floorboards refixed, screed made up, and plasterboard patched and set ready for decoration. Matching old tiles or a discontinued floor finish is not always possible and we say so before cutting rather than after. Ceilings that have taken a significant volume of water usually need the wet section cut out and replaced rather than dried in place, because saturated plasterboard loses its strength and sags.

Where the water has soaked into insulation, that insulation is finished. Wet mineral wool does not dry usefully in a closed void and it does not recover its performance. It comes out.

Does insurance cover a burst pipe, and what to record

Escape of water is one of the most common household claims, and it is the reason a burst is booked as an emergency plumber call out rather than as planned work, and most buildings policies deal with it in two parts: trace and access, which is the cost of finding and reaching the leak, and then the repair and the resulting damage. The pipe itself is often the smallest number on the claim. What your insurer means by trace and access is narrower than most people assume, and it is worth reading your own policy wording on it before the work starts rather than after the invoice arrives.

What insurers ask for is evidence, and the easiest time to gather it is while the water is still there rather than afterwards from memory. Photograph the damage before you mop. Photograph the burst pipe itself once it is exposed, and the opening before it is closed up. Keep any section of pipe that was cut out. Note the date and roughly when it started, and whether anyone had work done recently, including a neighbour.

We record what was found and where, and photograph the opening before it is closed, so you have something to submit rather than a description. Whether you claim at all is a judgement about the size of the damage against your excess, and it is your call, not ours.

How to stop the next burst pipe

Most repeat bursts are preventable and the preventions are dull. Lag the pipework in the loft, the garage and any unheated void, and lag the pipe itself rather than only the tank. Insulation that has slipped off a bend is insulation that is doing nothing, and bends are where pipes freeze.

Fit and use the isolating valve on the outside tap. Close it in autumn, open the tap itself and let the section outside drain, and leave the tap open through the winter. A split outside tap feed is one of the most common February calls and it is entirely avoidable.

If you are leaving the property empty in winter, either leave the heating on a low setting with the thermostat around 12 to 15 degrees, or drain the system down properly. Switching the heating off completely and locking the door is what produces the burst that runs for a fortnight before anyone notices.

Replace flexible tap connectors when you replace taps. The braided hoses under basins and behind washing machines have a rubber inner that perishes, and a failed one at mains pressure empties into a cupboard at a rate that will reach the flat below. They are cheap, they are quick to change, and they are the cause of a large share of the bursts that happen in properties where nothing has frozen and nothing is old.

• Lag loft, garage and void pipework, including the bends
• Isolate and drain the outside tap before the first frost
• Keep low background heat in an empty property in winter, or drain down
• Replace braided flexible tap connectors rather than leaving them indefinitely
• Exercise the main stopcock once or twice a year so it works when needed