What should I do if I have no water in freezing weather?

No water on a frosty morning is usually a frozen section in an unheated space. Finding it, thawing it slowly, and being ready for the leak when it thaws is the whole job.

Difficulty: beginner
Time: 1 hr
Read: 6 min
Safety: warning

Short answer

Turn the stopcock off first, so a burst does not flood the house when it thaws. Find the frozen section by following the pipe through cold spaces — loft, garage, outside wall, condensate pipe — and feeling for the cold, frosted part. Thaw it with warm towels, a hot water bottle or a hairdryer on low, working from the tap end back. Never use a flame, and never boiling water.

Water expands by about nine per cent when it freezes, and a closed section of pipe has nowhere to put it. That is why the damage almost always shows up during the thaw rather than the freeze: the ice has already split the pipe or pushed a joint apart, and nothing appears until the plug of ice melts and the water finds the hole. Pipes freeze where they run through unheated space, and the same few locations account for nearly all of them.

Safety

Never use a blowtorch, heat gun, gas burner or naked flame on a pipe. It is a common cause of house fires, it can boil water inside the pipe and burst it violently, and on a plastic pipe it fails instantly. Never use boiling water on a frozen pipe either — hot, not boiling. If a pipe has already burst, shut the stopcock first, switch off the electricity to any area where water is running near fittings, and ring a plumber.

What you'll need

Knowledge of where your internal stopcock is
Towels and a kettle of warm water, or a hot water bottle
A hairdryer, used away from any water (optional)
A torch
Buckets and a plumber's number
Pipe lagging, for afterwards

The pipes and fittings that freeze first

Step by step

Turn the water off at the internal stopcock first.Before you thaw anything. If the pipe has split, thawing it with the supply on floods the house. Usually under the kitchen sink; open a cold tap afterwards to relieve pressure.
Check whether it is your house or the street.Ask a neighbour, or ring the water company. A mains problem in freezing weather is common and is not something to chase around your own loft for an hour.
Look in the obvious cold places, in order.Loft pipes above the insulation, the cold water tank, the outside tap and its supply, an unheated garage or cellar, a porch, and any pipe on the inside face of an external wall. These are where it freezes.
Feel along the pipe for the frozen section.A frozen length is noticeably colder than the rest, often frosted or with condensation, and may be slightly bulged. Follow it from the tap that has no water back towards the source.
Thaw from the tap end back towards the frozen plug.Open the affected tap first so meltwater and steam have somewhere to go, then apply heat starting nearest the tap and working backwards. Heating the middle of a plug can trap expanding water and burst the pipe.
Use gentle heat only.Warm towels wrung out in hot water and rewrapped, a hot water bottle held against the pipe, or a hairdryer on a low setting kept moving and kept away from any water. Slow is safer and works just as well.
Never use a flame, a heat gun or boiling water.A blowtorch on a pipe in a loft is a leading cause of house fires. Boiling water can flash the ice to steam and split the pipe. There is no situation where either is the right tool.
Watch for the leak as it thaws.Stay with it. Have towels and a bucket ready. If water starts escaping, the stopcock is already off, which is exactly why that was step one.
Deal with a frozen boiler condensate pipe separately.A boiler that has locked out in a cold snap is very often a frozen condensate — the small white or grey plastic pipe running outside to a drain. Pour warm water over the external section, or wrap it in a warm cloth, then reset the boiler once.
Lag it properly once it has thawed.Foam lagging on every pipe in an unheated space, taped at the joints, with no gaps at bends and valves. Lag over and around a loft tank, never underneath it, so warmth from the house below still reaches it.

Tips

Lagging slows freezing; it does not prevent it in an unheated space. Anything that will be unheated for weeks — an empty holiday let, a shed supply, an outside tap — should be drained rather than lagged.
The outside tap is the most frequent single casualty. Turn the indoor isolating valve off and leave the outside tap open through winter so any remaining water can expand harmlessly.
Leaving the heating on a low continuous setting, around 12 to 15 degrees, while away in winter costs far less than a burst pipe, and most insurers require it or a full drain-down.
Open the loft hatch a little in a hard freeze so warm air reaches the loft. It is crude and it works.
If pipes freeze in the same place every year, that section needs rerouting or better insulation rather than an annual thaw. It is a small plumbing job with a large payoff.

Common mistakes

Thawing before shutting the stopcock — If the ice has already split the pipe, thawing it with pressure behind it releases the full flow into the house. Stopcock first, every time.
Using a blowtorch or heat gun — It sets fire to loft timber and insulation, melts plastic pipe instantly, and can burst a copper pipe by flashing trapped water to steam. This causes house fires every winter.
Heating the middle of a frozen section — Meltwater is trapped between two plugs of ice with nowhere to expand, which splits the pipe. Work from the open tap back.
Walking away once it has started to thaw — The moment of thaw is the moment a split reveals itself. Stay with it, with a bucket, for as long as it takes.

If it doesn't work

One tap has no water, the rest are fine

Cause: A frozen section on that branch, usually in a cold void — Fix: Follow that pipe back from the tap through any unheated space and thaw the cold section gently. If the pipe is inside a wall, warming the room and being patient is usually the only option.

No water anywhere in the house

Cause: Frozen at the rising main, the stopcock, or a mains supply problem — Fix: Check with the water company first. If the street is fine, thaw the rising main where it passes through an unheated space, working upward from the stopcock.

Boiler shows a fault and there is a gurgling noise

Cause: Frozen condensate pipe — Fix: Warm the external condensate pipe with warm water or a cloth, then reset the boiler once. Have the pipe re-routed internally or upsized if it happens repeatedly.

Water pours out as soon as the ice melts

Cause: The pipe or a joint has split — Fix: Keep the stopcock off, contain the water, and ring a plumber. A push-fit repair coupler is a reasonable temporary fix on a straight run for anyone confident; the joint still needs checking afterwards.

Questions people ask

How cold does it have to be for pipes to freeze?

Sustained air temperatures below freezing, especially for more than a day or two, and it is duration rather than the low point that matters. A single cold night rarely does it; three days at minus two in an unheated loft very often does.

Should I leave the taps dripping?

It helps a little because moving water freezes more slowly, but it is a weak measure compared with lagging, keeping the heating on low, and draining anything that will be unused. It also wastes water and is not a substitute for the real fixes.

Is a burst pipe covered by insurance?

Escape of water is a standard peril on most buildings policies, but insurers commonly exclude it in an unoccupied property where the heating was not left on or the system was not drained. Check the unoccupancy conditions before going away in winter.