How to Prevent Frozen Pipes, and How to Thaw Them Safely

Why pipes burst

When water freezes it expands by about 9 percent. Ice in a pipe pushes the remaining water towards the closed tap, and the pressure builds until the pipe splits. A crack of just a few millimetres can release hundreds of litres of water a day once it thaws.

The pipes most at risk are:

• Pipes in unheated spaces: lofts, garages, crawl spaces, basements and under-sink cabinets on outside walls.
• Outdoor taps and garden hoses, swimming pool and sprinkler lines.
• Pipes running along exterior walls with little insulation.

How to prevent frozen pipes

Before winter

1. Insulate exposed pipes with foam pipe sleeves from a hardware shop. They are cheap and quick to fit.
2. Disconnect garden hoses, drain outdoor taps, and turn off the indoor valve that feeds them if you have one.
3. Seal draughts near pipes, such as gaps around cables, vents and foundations.
4. Find your main water shut-off valve (the stopcock) and check that it turns. In an emergency you need to close it fast.

On freezing nights

1. Keep the heating on, even when you go away. Many plumbers suggest no lower than about 12°C (55°F) indoors.
2. Let cold taps drip on outside walls. A slow, steady drip is enough.
3. Open cabinet doors under sinks on outside walls, so warm room air reaches the pipes. Move cleaning products out of reach of children and pets.
4. Keep the garage door closed if water pipes run through it.

If a winter storm watch or warning is issued, do these steps before the cold arrives, and prepare for a possible power cut, since heating systems often stop with the power.

Signs a pipe is frozen

• You turn on a tap and only a trickle or nothing comes out.
• Frost on the outside of a visible pipe.
• An odd smell from a drain, because the water is not moving.
• A bulging section of pipe.

Work out which taps are affected. If only one tap has stopped, the frozen section is likely between that tap and where its pipe enters the house or runs along a cold wall.

How to thaw a frozen pipe safely

1. Open the tap the pipe feeds, both hot and cold. Flowing water helps melt the ice, and the open tap relieves pressure.
2. Warm the pipe gently, starting from the tap end and working back towards the frozen section, so meltwater can escape. Safe options:
   • a hair dryer
   • an electric heating pad wrapped around the pipe
   • towels soaked in hot water
   • a portable space heater kept well away from anything flammable, and never left unattended
3. Keep heating until full flow returns.
4. Check other taps for frozen sections too.

Never use a blowtorch, gas heater, charcoal stove or any open flame. They are a fire risk, can boil water in the pipe and make it explode, and indoor flames produce carbon monoxide.

Call a plumber if you cannot reach the frozen section, cannot find it, or the pipe is inside a wall.

If a pipe bursts

1. Turn off the water at the main shut-off valve immediately.
2. Turn off the electricity to affected areas if water is near sockets or the consumer unit, and only if you can reach the switch safely without standing in water.
3. Open all taps to drain the system and relieve pressure.
4. Mop up and move belongings out of the way. Mould can start within 24 to 48 hours.
5. Take photos for your insurer before you clean up, and call a plumber.

Home insurance often covers sudden burst-pipe damage, but may not if the home was left unheated and unoccupied for a long period. Check your policy before you travel in winter.

Key takeaways

• Pipes in unheated spaces and on outside walls freeze first.
• Heating on, cold taps dripping and cabinet doors open prevent most freezes.
• Thaw from the tap end with a hair dryer or heating pad, never a flame.
• Know where your main water shut-off valve is before you need it.

This article is general guidance. For pipes inside walls, gas appliances or electrical risks, call a qualified plumber or electrician.