Protecting Pipes From Freezing: A Winter Plan for Every Home

Frozen pipes are one of the few plumbing problems you can see coming. The forecast warns you about a cold snap, and the places where pipes freeze are much the same in almost every house. A couple of hours of preparation in autumn and a few habits in the coldest weeks prevent most of the damage. If you're already too late, the emergency steps are near the end.

Why a frozen pipe splits

Water expands by roughly a tenth as it turns to ice. Inside a pipe, the ice plug itself rarely does the damage. The trouble is the water trapped between the plug and a closed tap or valve. As more ice forms, the pressure in that trapped section climbs until a joint gives way or the pipe wall splits. That's why a burst often appears a short distance from the coldest spot, and why it usually announces itself only when the thaw arrives and water starts moving again.

Copper usually splits lengthways. Plastic pipe copes with freezing a little better, but push-fit joints can be forced apart.

Where pipes freeze

Lofts and roof spaces

A well-insulated loft is a cold loft, because the insulation keeps the house's heat below the ceiling. Any pipes or tanks above that insulation are, in practical terms, outdoors. Cold water storage tanks, small feed and expansion tanks and the pipes between them are the classic victims.

Pipes on or in outside walls

Kitchen sinks under a window, pipes boxed in against an external wall and runs at the back of a cupboard on a north-facing side all lose heat quickly. Gaps where a pipe passes through the wall let cold air blow straight onto it.

Garages, utility rooms and under floors

Unheated spaces holding a washing machine, a sink or a water softener are easily forgotten until the first hard frost. So are pipes under suspended timber floors, where airbricks let freezing air circulate around them.

Outside taps

An outside tap sits on a short pipe that runs straight through the wall. If water is left in that pipe it will freeze before almost anything else in the house, and the split often happens inside the wall where you can't see it.

The condensate pipe on a condensing boiler

Condensing boilers produce a slightly acidic water, called condensate, that drains away through a plastic pipe. If that pipe runs outside to a gully or soakaway, it can freeze during a long cold spell. The condensate then backs up and the boiler shuts down for safety, usually with a fault code and sometimes a gurgling noise. It looks like a breakdown, but the boiler itself is usually fine. The fix is further down.

Insulation: what to buy and how to fit it

Pipe lagging is a foam or mineral-fibre tube, slit along one side so it pushes over the pipe. Two measurements matter.

• Inside diameter. Match it to the pipe. Common domestic copper sizes are 15 mm and 22 mm in Britain and much of Europe, while North American homes typically use half-inch and three-quarter-inch. Lagging that's too big leaves an air gap; too small and the slit won't close.
• Wall thickness. Thicker insulates better. Thin lagging is fine inside heated rooms. In a loft, garage or floor void, use the thickest that fits the space.

Fitting tips:

• Cover the whole run, including bends, tees and valves. Cut the tube at 45 degrees to make neat corners instead of leaving bare joints.
• Tape every seam and butt joint with insulation tape so the slit doesn't creep open as the foam ages.
• Keep valve handles and stopcocks reachable by leaving a short removable section.
• In the loft, lay the main insulation over the pipes, never between the pipes and the ceiling. The pipes should benefit from the warmth rising through the ceiling.
• Insulate cold water tanks on the top and sides with a tank jacket or rigid board, but leave the patch of ceiling directly under the tank uninsulated, for the same reason.
• Outside, use weather-resistant lagging and a purpose-made insulated cover for the tap.

Heating settings that protect pipes

Your heating is the best frost protection you have, provided it's set up for the job.

• Frost setting. Many boilers, programmers and room thermostats have a frost-protection mode, often marked with a snowflake. It fires the heating when the temperature falls to a low threshold, usually a few degrees above freezing. Check the manual, because some protect only the boiler, not the house.
• Radiator valves. Use the snowflake setting on thermostatic radiator valves in spare rooms rather than turning them fully off.
• During a cold snap. Running the heating low for longer is gentler on exposed pipes than switching off overnight and blasting it at six in the morning. Open the doors of sink cupboards on outside walls so warm air can reach the pipes, and on the very coldest nights consider leaving the loft hatch open for a few hours.
• When you go away. Leave the heating on at a low, steady temperature rather than off. Read your home insurance policy too. Many have conditions about heating an unoccupied home or draining it down, and a claim for a burst can be refused if they weren't followed.

If the house will stand empty

For a holiday home, a property between tenants or a house sitting unsold over winter, draining the water down may be safer than heating an empty building. A typical sequence:

1. Switch off the boiler, water heater or immersion heater at its power supply first. Heating appliances must not run dry.
2. Close the main stopcock.
3. Open every cold tap, starting at the top of the house and finishing with the lowest, and leave them open.
4. Open the hot taps in the same order.
5. Flush each toilet and hold the handle down until the cistern is empty.
6. If there's a drain-off valve just above the stopcock, run a hose from it to a drain and open it to empty the rising main.
7. Leave a note at the stopcock and boiler: system drained, refill before switching anything on.

Draining a hot water cylinder or a sealed central heating circuit is a different matter. Some heating systems are better protected by adding a suitable antifreeze inhibitor than by emptying them, and anything involving an unvented cylinder or a gas appliance needs a qualified heating engineer. Who is allowed to do what varies by country.

Pre-winter checklist

Work through this in early autumn. It slots neatly into a wider home plumbing maintenance calendar.

• Find the main stopcock, label it, and turn it off and on once to prove it moves.
• Check lagging in the loft, garage and under floors. Replace anything crushed, damp or missing.
• Fit or check the jacket on any cold water tank.
• Close the indoor isolating valve for the outside tap, open the tap to drain it, fit an insulated cover and bring hoses inside.
• Follow the boiler's condensate pipe outside and note whether its exposed section is insulated.
• Set the frost protection on the boiler or thermostat and confirm it's active.
• Check the boiler pressure gauge reads within its normal range with the system cold.
• Save your insurer's emergency number in your phone and note the policy's rules for unoccupied homes.

When a pipe has frozen

The signs are usually obvious: a tap gives nothing or a thin trickle on a cold morning, a cistern refuses to refill, frost is visible on a pipe, or the boiler locks out with a condensate fault.

1. Close the stopcock. Even if you can't see a split, a damaged pipe will only start leaking once it thaws.
2. Open the tap the frozen pipe feeds. That gives melting water somewhere to go and relieves the pressure.
3. Find the frozen section. It's normally in the coldest, least insulated part of the run.
4. Warm it gently, starting at the tap end and working back towards the ice. Use a hairdryer on a low setting, a hot water bottle, or towels soaked in hot water and wrung out. Keep the hairdryer and its cable away from any water.
5. Be patient. A stubborn plug can take half an hour or more to clear.
6. When water flows, inspect the run, especially the joints, before opening the stopcock fully. Then keep checking for drips over the next hour or so.

For a frozen condensate pipe, pour warm (not boiling) water along the outside section, or hold a hot water bottle against it, concentrating on bends and the open end where ice tends to build up. Then reset the boiler following the manufacturer's instructions. If the pipe freezes every winter, ask a heating engineer about rerouting it indoors or improving the external run. If the boiler won't restart, or the gauge has dropped after all the fuss, our guide to a combi boiler losing pressure explains the next checks.

Burst pipe: emergency procedure

1. Shut off the water at the main stopcock. If it won't budge, look for an isolation valve closer to the leak or, in a block of flats, a valve in the communal area.
2. Think about electricity. If water is near sockets, light fittings or the consumer unit, switch off at the main switch only if you can reach it without standing in water or touching anything wet. If you can't, keep clear and call an electrician or your electricity network's emergency line.
3. Turn off the boiler and any water heater.
4. Drain the pipes by opening cold taps and flushing toilets, so less water escapes through the burst.
5. Catch and contain with buckets, bowls and towels. Move rugs, furniture and electronics. If a ceiling is sagging, keep everyone out of the room below.
6. Warn the neighbours if you live in a flat.
7. Photograph and film everything before tidying up: the burst, the water, damaged ceilings and belongings. Note the time.
8. Call your insurer and follow their process before agreeing to major repair work.
9. Get the pipe repaired by a competent plumber, and have any electrics that got wet checked by an electrician before using them.

After a burst, moisture can linger in walls and under floors long after the visible water is gone. If stains come back or the meter moves with everything turned off, our water leak detection guides cover how to track down what's left.

What not to do

• Don't use a blowtorch, a heat gun on a high setting or any naked flame to thaw a pipe. It's a fire risk, it can damage soldered and plastic joints, and it can flash water to steam inside a sealed section.
• Don't pour boiling water over plastic pipe or a frozen condensate pipe.
• Don't switch the heating off completely during a cold spell to save money if you have pipes in unheated spaces.
• Don't touch switches, sockets or appliances while standing in water.
• Don't hammer, twist or try to bend a frozen pipe.
• Don't assume it's over once the ice melts. Check for leaks for the rest of the day.