Preventing Frozen Pipes During Cold Spells

Why a frozen pipe so often becomes a burst pipe

Water expands as it freezes, and it does so with surprising force. When the water inside a pipe turns to ice, that expansion has to go somewhere, and it usually pushes against the pipe wall or the joints at either end. The frustrating part is that the pipe often splits while frozen and only starts leaking once it thaws, which is why so many people discover the damage hours after the coldest point of the night. By then, water may have been running into a ceiling, behind plasterboard or under a floor for some time.

A single burst can mean a soaked ceiling, ruined flooring, damaged electrics and a hefty insurance claim. The good news is that frozen pipes are one of the most preventable winter problems in a typical British home, and the work involved is modest — mostly lagging and a bit of forethought about your heating.

Which pipes are actually at risk in your home

Pipes running through heated living space rarely freeze. The trouble spots are the cold, draughty and overlooked parts of the property. Have a proper look at these before the first hard frost:

• Pipework in the loft, especially running close to eaves where cold air blows through
• The cold water tank and its connecting pipes, if you still have one
• Pipes in an unheated garage, outbuilding, cellar or coal hole
• Any pipe running along an external wall, inside a cupboard on an outside wall, or under a suspended floor
• Outdoor taps, garden irrigation lines and their supply pipes
• The condensate pipe from a condensing boiler, usually a white plastic pipe running outside to a drain

Condensate pipes catch out a huge number of households every winter. When they freeze, the boiler locks out and you lose both heating and hot water at exactly the moment you need them most. If yours runs outside, it is worth treating it with the same care as any other exposed pipe.

Lagging exposed pipework properly

Foam pipe insulation — often sold as lagging — is cheap, and it takes minutes to fit. Buy the correct diameter for your pipe, usually 15mm or 22mm, and make sure the wall thickness is generous rather than the thinnest option on the shelf. Measure the runs first so you buy enough.

• Slide the lagging on so the slit faces downwards, away from rising warm air and any drips
• Butt the lengths tightly together and seal the joints with tape rather than leaving gaps
• Insulate hot and cold pipes alike — hot pipes freeze too, and lagging cold pipes also stops condensation
• Pay extra attention to bends, elbows, valves and joints, which are the first places to fail
• Wrap the cold water tank itself with a jacket, but leave the loft floor beneath it free of insulation so warmth can still rise

For pipes in genuinely exposed spots, such as an outside run or a draughty outbuilding, consider a length of trace heating cable, which warms the pipe gently when temperatures drop. Fit it according to the manufacturer's instructions and have it checked by an electrician if you are unsure.

Keeping the heating on low — the balancing act

This is the single most effective habit for cold spells. Rather than switching the heating off overnight or while you are out, leave it running at a low background temperature. Somewhere between 12°C and 15°C is usually enough to keep the fabric of the house and the pipework above freezing without wasting money. It costs far less than repairing a burst.

If you have a programmer or smart thermostat, set a frost protection or "away" mode rather than turning everything off. Check that the boiler's own frost thermostat, if fitted, is working. During a severe snap, open the loft hatch for an hour or two each day so a little warmth drifts up into the roof space, and leave cupboard doors open where pipes run along external walls.

Fix dripping taps and overflowing cisterns before winter. A slow trickle through a trap or a pipe is far more likely to freeze than still water in a well-insulated run, and it wastes water all year round.

If you are going away during a cold snap

Empty homes cool down fast and lose the benefit of any background heating. If the property will be empty for more than a few days in freezing conditions, either leave the heating on its lowest setting or drain the system down properly. Turn off the stopcock, open the taps to release pressure, and consider draining the cold water tank and any exposed runs. Ask a neighbour or family member to check the house, or use a smart thermostat and a leak sensor so you can react quickly from wherever you are.

Thawing a frozen pipe safely

If you turn on a tap and nothing comes out, or the flow is a trickle when it should be strong, suspect a frozen pipe. Turn off the stopcock immediately and open the nearest cold tap so that melting water has somewhere to go.

Thaw the pipe gently, working from the tap end back towards the frozen section, using a hot water bottle, warm towels or a hairdryer on a low setting. Never use a naked flame or a blowtorch, and never pour boiling water directly onto a pipe or a plastic fitting. Once the water runs freely again, check the whole run carefully for splits or weeping joints — a pipe that froze has been stressed. If you find damage, or you cannot locate the blockage, call a qualified plumber rather than improvising.