How to stop pipes freezing this winter

When water freezes inside a pipe it expands, and that can split the pipe or a joint. Often you don't find out until the thaw, when water starts pouring through a ceiling. A few cheap jobs in the autumn make this much less likely, and most of them take less than an hour.

Which pipes are most likely to freeze?

Pipes in heated rooms rarely freeze. The ones at risk are those in cold, unheated spaces or exposed to the outside air. Thames Water lists pipes leading to outside taps, unheated lofts, garages and utility rooms as the most vulnerable. Also check:

• Pipes and water tanks in the loft, especially above the insulation.
• Pipes that run along or through outside walls.
• Outside taps and garden pipework.
• The water meter cupboard, if your meter is in an outside box or a cold cupboard.
• Pipes under floors, in cellars or in empty rooms you don't heat.

How do I prevent frozen pipes with lagging?

Lagging is foam insulation that wraps around a pipe. It's the single most useful thing you can do to prevent frozen pipes. Thames Water says foam lagging from DIY stores usually costs around £1 a metre, so doing a whole loft is rarely expensive.

1. Measure the pipes you want to cover and buy lagging that matches their width.
2. Push the foam over each pipe so the split closes fully, and tape the joins so there are no gaps.
3. Cover bends and joints as well as straight runs. Gaps are where pipes freeze first.
4. Use waterproof lagging for any pipes outside, as United Utilities advises.
5. Insulate cold water tanks in the loft too. The Association of British Insurers recommends insulating loft pipes and tanks.

If your water meter sits in a cupboard or box, United Utilities suggests packing the space with insulation and lagging the pipes that lead into it.

How do I protect an outside tap in winter?

Outside taps are the most common thing to freeze because they sit in the open air. WaterSafe, the UK register of approved plumbers, recommends you:

• Disconnect, drain and put away the hosepipe before the frosts start.
• Turn off the supply to the outside tap if it has its own shut-off valve. This is often on the pipe inside, near where it goes through the wall.
• Open the outside tap after shutting it off, so the water left in it can drain out, then close it again.
• Fit an insulated tap cover and lag any exposed pipe leading to it.

If your outside tap has no shut-off valve, a cover and lagging still help a lot. A plumber can fit a valve for you so the tap is easier to protect next winter.

Should I leave the heating on to stop pipes freezing?

In a cold spell, some heat in the house protects the pipes. You don't need it on full. United Utilities advises keeping the heating on low or on a frost setting when you're away, and the ABI suggests setting the heating on a timer if you go away.

• Smart thermostats often have a frost or anti-freeze mode that keeps the house at a low minimum temperature.
• Some radiator valves have a snowflake setting. The ABI says this frost setting keeps a minimal flow of water through the radiator.

If you'll be away for a long time, turning the water off at the stop tap can be a good precaution. United Utilities says to check with a qualified heating engineer first, because on some systems this can affect the heating.

Where is my stop tap and does it work?

Your stop tap, also called a stopcock, turns off the water to the whole house. If a pipe freezes or bursts, finding it quickly limits the damage. It's usually under the kitchen sink, but it can be in a downstairs toilet, garage, utility room or cellar.

Find it now, before you need it. The ABI recommends testing it too. Turn it clockwise to close it and check a cold tap stops running, then turn it back on. If it's stiff, seized or won't fully shut off the water, ask a plumber to look at it before winter.

What to do if your pipes have already frozen

Signs of a frozen pipe include no water, or only a trickle, from a tap, and frost on the outside of a pipe. Thames Water's advice is to thaw it slowly:

1. Turn off the water at the stop tap.
2. Open the tap fed by the frozen pipe, so water can escape as it thaws.
3. Remove any lagging from the frozen section and move furniture and valuables out of the way.
4. Warm the pipe gently with a hot water bottle or warm towels.
5. Once it's thawed, run a dry cloth along the pipe. If the cloth gets wet, there's a split, so leave the water off and call a plumber.

Never use a blowtorch or any naked flame, and don't hit the pipe to break the ice. The ABI warns against both, because they can damage the pipe or start a fire.

What to do if a frozen pipe bursts

A split pipe can stay hidden until the ice thaws. After a cold snap, Thames Water suggests checking pipes in cold places such as the loft and garage for drips. If you find a burst:

Safety: If water is leaking near sockets, lights, the boiler or the consumer unit, keep away from the wet electrics and don't touch them. Only switch the power off at the consumer unit if you can reach it without standing in or touching water. If you can't, leave the area and get help.

1. Turn off the water at the stop tap.
2. Switch off the heating.
3. Open all the taps to drain the system faster, keeping a bucket of water aside for flushing the toilet.
4. Soak up water with towels and move belongings out of the way.
5. Call a plumber, and contact your home insurer if there's damage.

Our guide to stopping a burst pipe safely covers these steps in more detail. If the leak is in the road or pavement rather than your home, report it to your water company. In Berkshire that depends on where you live, and the name is on your water bill.

When should I call a plumber?

Lagging pipes and covering outside taps are easy jobs to do yourself. Call a plumber if a pipe has split, if a frozen pipe won't thaw or is somewhere you can't reach safely, if your stop tap is seized, or if you'd like a shut-off valve fitted for an outside tap. WaterSafe recommends using an approved plumber, such as one on its register.

Thames Water also suggests keeping the number of a qualified emergency plumber handy before winter, so you're not searching for one with water coming through the ceiling.