Frozen and burst pipes: prevent, thaw, and act fast

Why pipes burst — and why it's worth preventing

It's counter-intuitive, but a frozen pipe doesn't leak while it's frozen — it bursts when it thaws. Water expands as it freezes, and with nowhere to go the ice pushes against the pipe until it cracks or splits; then, as it melts, water pours out of the split. The risk starts at 0°C and climbs through prolonged sub-zero spells, especially for pipes in unheated lofts, garages and outdoors.

This is not a rare event to shrug off. 'Escape of water' — which includes burst and frozen pipes — is one of the most common home-insurance claims in Britain, with insurers paying out around £1.8 million every single day, and the Association of British Insurers puts the average cost of repairing a burst pipe at about £8,800. A few pounds of prevention genuinely saves a five-figure mess.

Prevention 1: keep the heat ticking over

The simplest defence is to not let the house get cold enough to freeze the pipes. In a cold snap, and especially if you go away, leave the heating on low rather than off. British Gas advises keeping the thermostat set to at least 7°C even when the house is empty — enough to keep the chill off the pipework without heating an empty home to full temperature.

It's a small running cost against the risk of a burst pipe and a ruined ceiling — comfortably the better trade.

Prevention 2: lag the pipes, and find your stopcock

Insulate exposed pipes and water tanks with cheap foam pipe lagging from any DIY shop, prioritising the coldest unheated spots where freezing starts — the loft, the garage, and any outdoor pipework. If pipes or a tank sit in an unheated loft, open the loft hatch during icy weather so warm air from the heated house below can rise and take the edge off.

Then the single most important thing: find your internal stop tap (stopcock) — usually under the kitchen sink, or where the mains pipe enters the house — and check that it actually turns before you ever need it. That one valve is what stops water flooding the house if a pipe bursts, and you don't want to be hunting for a seized-up tap in an emergency.

If a pipe freezes

Caught it before it burst? Turn the water off at the stop tap straight away, and open the nearest tap to relieve the pressure and give the melting ice somewhere to go. Then thaw the pipe gently, starting at the end closest to the tap and working back, using a hot cloth, a hot water bottle or a towel soaked in hot water.

Never use a naked flame or a blowtorch to thaw a pipe — it's dangerous and the sudden heat can crack the pipe and make things far worse.

If a pipe bursts

Act fast to limit the damage. Turn the water off at the stopcock immediately and leave it off until a plumber has repaired the pipe. Switch off the central heating (and any water heating), then open all the taps to drain the system quickly. Soak up escaping water with towels, and if any electrics might have got wet, turn the power off at the mains — never touch wet electrics.

Then call a fully qualified plumber and your insurer. Burst pipes are exactly what home insurance's 'escape of water' cover is for, so document the damage with photos before you clear up.

Ask your water company first

Before you pay for a repair, work out where the leak is, because that decides who pays. Your water company is responsible for the water main and the communication pipe that joins it to your supply pipe. The underground supply pipe from your boundary into the house, and all the plumbing inside, belong to the property owner; if you rent, repairing them is usually your landlord's job. The water company won't repair a burst in the loft or under the sink.

A leak on that underground supply pipe is where your water company may help. The Consumer Council for Water (CCW) advises asking your company whether it offers one-off help to find and repair a supply-pipe leak, and says the conditions vary from company to company. Southern Water, for example, offers a free leak detection visit of up to an hour when a leak is suspected below ground, and Yorkshire Water says customers registered on one of its financial support schemes may qualify for a free supply pipe repair. If the leak is underground, ask before you book a plumber.

If you're on a water meter, ask for a leak allowance once the leak is fixed. CCW says your company should offer a one-off allowance for the lost water, and suggests asking your sewerage company for an allowance too, for water that drained into the ground rather than the sewer. The rules differ, and after a freeze they matter: United Utilities accepts claims for a leak on internal or external pipework, while Southern Water makes no adjustment when the leak came from faulty pipes or fittings inside your home. The companies we checked want the repair done within about four weeks (30 days at United Utilities, 30 days at Southern Water for the full allowance, four weeks at Thames Water), so fix it promptly, keep the plumber's invoice and claim straight away: Yorkshire Water wants the claim within 28 days of the repair (or of asking it to investigate), and Thames Water and Southern Water set a three-month limit. CCW also suggests checking whether your contents insurance covers the cost of lost metered water.