Burst Pipe

What's happening?

A burst pipe is a split or blown joint in pressurised pipework, so water keeps pouring out until someone closes a valve upstream of it. Mains-fed cold pipework is the worst case because it is fed straight from the street at full pressure and cannot run dry. Most UK bursts happen for one of two reasons: water froze inside the pipe, expanded and split the wall, or a nail or screw went through a pipe buried in a wall or under a floor. Copper splits along its length; plastic push-fit tends to blow the joint instead. The damage is rarely the plumbing — it is the ceiling, floor and contents underneath.

What usually causes it?

• Water freezing in an unlagged pipe in a loft, garage or outside wall, expanding and splitting the copper
• A nail, screw or floorboard pin driven through a pipe buried in a wall or under floorboards
• A push-fit or compression joint that was never fully made and has finally let go
• Corrosion pinholing an old copper or low-quality pipe run, often near a soldered joint
• Excessive mains pressure with no pressure-reducing valve, stressing joints over years
• Ground movement or vibration pulling a joint apart on a buried supply pipe

When should you call a plumber?

Call a plumber as soon as the water is off — a burst is a same-day job, not something to leave over a weekend, because the house has no water while the stop tap is closed. Call immediately, before anything else, if water is running near electrics, coming through a ceiling, or you cannot stop the flow. If the leak is in the supply pipe outside your boundary or in the street, that is your water supplier's pipe and their emergency line, not a plumber's job.

What will the plumber actually do?

• Isolate the affected section, drain it down and confirm where the water is actually coming from rather than where it is showing
• Cut out the split section and remake it in copper or push-fit, or replace a failed joint
• Pressure-test the repaired run and check the rest of the circuit for other frost damage
• Refill, vent air out of the system and re-commission the hot water and heating
• Lag exposed pipework in the loft, garage or against outside walls to stop it happening again
• Advise on a pressure-reducing valve or an accessible replacement stop tap where the old one is seized

Turning the water off, in order

1. Close the internal stop tap clockwise until it stops.
2. Open every cold tap in the house and flush the toilets to empty the pipework.
3. Switch off the boiler, and any immersion heater, at its own switch.
4. Leave hot taps closed until the hot water system has cooled and stopped heating.
5. If the stop tap fails, use the external stop valve at the boundary or call your water supplier.