Frozen pipes: how to prevent and safely thaw them

Pipes freeze where they're exposed to cold air: in lofts, garages and outbuildings, under suspended timber floors, along outside walls and in the pipe to an outside tap. London winters are usually mild, but a few nights well below freezing are enough, and many older houses have pipework in unheated lofts and draughty voids.

Water expands as it freezes. That can split a pipe or push a joint apart, and the leak often doesn't show until the ice thaws, sometimes hours later.

• Lag exposed pipes in the loft, the garage and under the floor with foam pipe insulation, covering bends and valves as well as the straight runs. We can lag pipes for you if they're hard to reach.
• If you have a cold water tank in the loft, insulate its top and sides, but leave the loft insulation directly underneath it clear, so a little warmth from the house below can reach it.
• In very cold spells, keep the heating on low, or use the frost setting on your boiler or thermostat if it has one, even when you're out or away.
• On the coldest nights, open the loft hatch and the doors of any cupboards with pipes inside, to let warm air reach them.
• Before winter, close the indoor isolation valve for each outside tap, then open the outside tap to let the water drain out. An insulated tap cover adds extra protection.
• Fix dripping taps and overflows, as a steady drip can freeze inside a waste or overflow pipe.
• If a property will be empty for a long spell in winter, keep the heating on low or have the water system drained down.

• No water, or only a trickle, from a tap after a freezing night
• A toilet cistern that won't refill
• Frost on a pipe, or a pipe that's much colder than the others
• A condensing boiler that shows a fault code or gurgles in cold weather (see the condensate pipe section below)

1. 1Turn off the water at the stopcock. A frozen pipe may already be split, and it will only start leaking as it thaws. Our guide to finding your stopcock explains where to look.
2. 2Open the tap fed by the frozen pipe, so water can escape as the ice melts.
3. 3Find the frozen section. It's usually the part in the coldest spot, such as where the pipe runs through the loft or along an outside wall.
4. 4Warm the pipe gently, starting at the tap end and working back towards the frozen section. Use a hot water bottle, towels soaked in warm water, or a hairdryer on a low setting, kept moving and well away from any water.
5. 5Check the pipe for splits, bulges or drips as it thaws. Once it has thawed, turn the stopcock back on slowly and look again for leaks.

1. 1Turn off the water at the stopcock straight away.
2. 2Open the cold taps to drain the pipes, and switch off the boiler and any immersion heater.
3. 3If water is near electrics, switch off the electricity at the consumer unit, but only if you can reach it safely while standing somewhere dry.
4. 4Move valuables, put down buckets and towels, and keep away from any ceiling that's sagging.
5. 5Call a plumber to repair the burst pipe.

Most gas boilers fitted since the mid-2000s are condensing boilers. They drain waste water through a plastic condensate pipe, usually white or grey, which often runs outside to a drain. In freezing weather that pipe can freeze, the water backs up and the boiler shuts down, often with a fault code or a gurgling noise.

If the outside section is safe to reach at ground level, you can usually thaw it by slowly pouring warm water, not boiling water, along it, paying most attention to bends and the open end, where ice tends to form first. A hot water bottle or a warm cloth held against the pipe works too. Then reset the boiler as its manual describes.