A burst pipe in a house is a bad day. A burst pipe in a mansion block is a bad day for several households, an insurance file, and quite often a dispute about who pays for a ceiling. The plumbing part is usually the simplest element. Everything around it — whose pipe it is, who can turn it off, whose ceiling it landed on, and which policy responds — is where these jobs actually get complicated.
This page covers the first hour, the ownership question that decides everything afterwards, and what the repair and the aftermath involve in the Edwardian and interwar block stock that fills W1, W2, NW8 and W9.
The first hour
Order matters more than speed here.
One. Get the water off. Your flat stopcock first — commonly under the kitchen sink, in an airing cupboard, or in a hall service cupboard. Closed is clockwise. Then open every tap in the flat, hot and cold, to drain what is already in the pipes. If you have a gravity system fed by a tank in the roof, there is a useful volume of water above you that will keep coming until it has somewhere to go, so draining down actively is not optional.
Two. If your stopcock does not stop it, it is not your pipe. This is the moment to call the porter, not to keep looking. If closing your flat's supply makes no difference to the flow, the water is coming from a communal riser, from a pipe serving another flat, or from something above you. You cannot fix that from inside your own front door.
Three. Deal with electrics. Water and a consumer unit is the point at which the priority stops being your floor. If water is running near a fuse board, near light fittings, or down inside a wall with cables in it, treat the circuit as unsafe. Do not switch things on to test them.
Four. Warn downwards. Knock on the door below before you have a diagnosis, not after. Water finds the path of least resistance and that path is almost always down through a joist void and out at the nearest light fitting. Giving your neighbour twenty minutes to move a rug is worth more goodwill than any apology later.
Five. Photograph everything. Before you mop, before anything is removed, before the ceiling is opened. This is not paranoia. It is the difference between a straightforward claim and a long argument.
Only then start thinking about the repair. If this is live and you have no water and no idea, our guide to calling an emergency plumber in Central London sets out how attendance actually works, including the access problems specific to blocks.
Why isolation is harder in a block than anywhere else
The awkward truth about mansion blocks is that the valve you need is frequently not yours to touch.
Most blocks distribute water vertically. Cold rises through a communal riser, often in a duct or a boxed corner, and each flat is teed off it. Somewhere there is an isolation valve for that riser. It might be in a locked cupboard on the landing, in the basement, in the roof tank room, or — in the genuinely unhelpful cases — inside another flat, behind a kitchen unit that was built in front of it in 1994.
Closing a riser affects every flat on it. That is why porters and managing agents keep control of it, and why a leaseholder who takes it upon themselves to shut a riser at midnight can end up in a difficult conversation. It is also why the practical answer, when your own stopcock does not stop the water, is the porter's number rather than a torch and some optimism.
What is worth doing now, before anything bursts: find out whether your block has a porter, what the out-of-hours arrangement is, and whether anyone holds a plan of the risers. Ask the managing agent. Many blocks have surprisingly good records; some have none at all. Either answer is useful to know in advance. Our guide to shared riser plumbing in mansion blocks goes into how these systems are usually arranged and where the demise boundary tends to sit.
Whose pipe is it? The question that decides the money
Almost everything that follows a burst — who repairs it, who pays, whose insurer picks up the damage — turns on one thing: was the failed pipe inside your demise, or was it part of the common parts?
The general position in most flat leases is that pipework serving only your flat, within your flat, is yours, and pipework serving more than one flat — risers, communal stacks, mains distribution — is the freeholder's responsibility as part of the common parts. But the wording varies genuinely and materially between leases, and there are plenty of leases where the boundary sits in an unexpected place. Some are silent on pipes in floor voids between flats, which is exactly where bursts happen. You need to read your own lease, or have your managing agent confirm, rather than rely on a general rule.
The same applies to insurance. Escape of water damage between flats usually engages the building's insurance, and in most blocks that policy is arranged by the freeholder or managing agent and paid for through the service charge. Your contents policy typically deals with your own belongings. Who bears the excess, and whether anyone pursues the leaseholder whose fitting failed, depends on the policy wording and the lease. Do not assume; ask the managing agent early and in writing.
What you can control is the record. Report it to the managing agent the same day. Confirm in writing what time you noticed it and what time it was isolated. Keep the failed component. Keep the plumber's written diagnosis. If it turns out to be communal, that paperwork is what moves the cost off you.
Why the pipes in this stock fail
Bursts here are not random.
Age and mixed metals. A 1930s block has typically been re-plumbed in patches for ninety years. Lead into copper, copper into galvanised steel, plastic spliced into copper by somebody in a hurry. Dissimilar metals in contact corrode, and the failure appears at the joint, usually at the least accessible point on the run.
Old joints under stress. Compression joints that were fine for decades let go after a floor is lifted, a unit is dragged across a board, or a new appliance is fitted three metres away. A surprising number of bursts happen shortly after unrelated work in the building.
Cold. Pipes in roof voids, unheated tank rooms, and cold risers on external walls freeze. In a block, the roof space is the classic location, and the classic timing is the first hard frost after a mild autumn. The damage is often done when it thaws.
Pressure changes. Where a block has been converted from gravity to mains-fed, or a booster has been added, old pipework that was designed for a couple of metres of head is suddenly seeing mains pressure. It survives until it does not.
Corrosion inside old steel. Galvanised runs close up internally and thin from the inside. Nothing is visible until the wall of the pipe fails.
Understanding which of these it was matters, because it tells you whether you have had a bad day or whether the rest of the installation is on the same clock.
The repair itself
Once the water is off, the actual repair is usually not dramatic. Cut out the failed section, replace it in a suitable material with proper joints, test, and refill slowly while watching everything else on the run — refilling a drained system is when the next weak joint tends to announce itself.
The real questions are about scope. If the failure was age-related, replacing a 300mm section of a five-metre run of tired pipe is a false economy: you will be back. If the floor is up anyway, the marginal cost of replacing the whole run is small compared with the cost of opening the floor a second time. We will always give you both options and be clear about which one we think is right, but the decision is yours.
If the pipe that failed is lead, that changes the conversation — see our guide to lead pipe replacement in London. If the burst has exposed the fact that the flat's supply is generally poor and old, our page on low water pressure in a London flat covers how that tends to present.
Access, consent and the block's rules
Three things reliably shape how a burst repair runs in this stock.
Getting to the pipe. Risers are boxed in. Floors have been tiled over, twice. Kitchen units have been built across access. In listed blocks and in conservation areas, cutting into original fabric can engage listed building consent where it affects the building's special character. An emergency repair to stop water is one thing; a planned re-route through protected fabric is another, and it needs the right permissions rather than an assumption.
Consent for anything beyond like-for-like. Most leases require freeholder or managing-agent consent for alterations, often through a licence to alter, and altering the route of waste or supply pipes is a typical trigger. Replacing a failed length as it was is normally repair. Moving it is normally alteration. Confirm which you are doing before you do it.
Hours and noise. Blocks commonly restrict noisy contractor work to weekday daytimes. Stopping a live leak is usually treated differently to planned works, but the rule belongs to your building — ask your porter or agent so you are not negotiating it with a saw in your hand.
These constraints are why we work the way we do across blocks in Marylebone, Maida Vale and St John's Wood: establish access and consent before committing to a scope, rather than discovering the problem with a floor open.
Afterwards: drying, making good, and the ceiling below
The plumbing is the short part. What follows takes longer than anyone expects.
Water that has gone through a floor is in the joists, in the plaster, and in the void. Making good a ceiling that is still wet gives you a stained, cracked ceiling and a second bill. Proper drying takes time and, in a bad case, equipment. It is worth insisting on it, particularly if an insurer is involved, because the cost of doing it properly is usually theirs and the cost of doing it twice will find its way to you.
Then reinstatement — ceilings, plaster, decoration, possibly flooring. Where a bathroom or kitchen floor had to be opened, there is tiling to reinstate, and in period stock the original tiles are usually unavailable. That is worth confronting early; our tiling page covers matching and reinstatement, and if the room has to come apart anyway, it can be the moment to think about a bathroom refurbishment rather than a patch.
If the burst revealed that the block's installation is generally at the end of its life, and the remedy is significant communal works, leaseholder consultation under Section 20 of the Landlord and Tenant Act 1985 may apply where the cost exceeds the statutory threshold per leaseholder. How and when that runs is for your managing agent to confirm.
How we work on these
Stop the water, find the cause, tell you plainly whether it is inside your demise or not, and put that in writing so you have something to send the managing agent. Then a fixed price for the repair before we start. Our plumbing work starts from £80 for attendance and diagnosis, and if the honest answer is that the failure is communal and not your bill, we will say so.
For blocks where this keeps happening, the better answer is planned rather than reactive — our maintenance service exists for that, and if you manage a portfolio, our page for agents and managers explains how we work with you. Send us photos through the quote form, or reach a plumber in Marylebone or Maida Vale the same way.