Frozen Pipes — How to Prevent Them and Safely Thaw Them

To prevent frozen pipes, lag everything in the loft, garage and outside walls, keep the heating ticking over on the coldest nights, and drain outside taps before winter. To thaw a frozen pipe safely: shut off the stopcock, open the affected tap, and apply gentle heat — warm towels, a heat pad or a hairdryer on low — starting at the tap end and working back. Never use a naked flame.

Why frozen pipes matter

Water expands by about 9% when it freezes. If that expansion happens inside a sealed length of copper or plastic pipe, the pressure has nowhere to go and the pipe splits. The split doesn't usually leak straight away — it leaks when the ice thaws. That's why burst pipes typically flood houses in the days after a cold snap, not during it. The whole point of prevention is to avoid putting yourself in the middle of that sequence.

Preventing frozen pipes

1. 1

   Lag every exposed pipe

   Foam pipe insulation costs pennies a metre. Cover lofts, garages, outhouses, the cold tank and the cold feed in particular. Don't forget the back of an external tap on an inside wall.

2. 2

   Keep the heating on overnight

   When the forecast drops below freezing, set the heating to a low background — 12-15°C through the night is enough. The savings from turning it off are far less than the cost of a single ceiling repair.

3. 3

   Isolate and drain outside taps

   Most outside taps have an inside isolation valve. Close it in autumn, then open the outside tap to drain the pipe. Frost-proof outside taps already drain themselves but check yours is one.

4. 4

   Drip a tap if you're worried

   Moving water freezes much later than still water. On a brutally cold night, leave the coldest tap (often a bath cold fed from a loft tank) running at a thin trickle.

5. 5

   If you're going away

   Either leave the heating on a frost-protection setting (around 7°C) or shut off the stopcock and drain the system. Don't leave a cold house full of standing water in January.

How to thaw a frozen pipe

If a tap or two has gone off in cold weather and the rest of the house still has flow, one pipe has frozen. Find it before you do anything else.

Find the frozen section

• Trace the dead pipe back from the tap that's stopped working.
• Run your hand along it — a frozen section will feel noticeably colder, and may look frosted or beaded.
• Common spots: lofts, the corner of an outside wall, garages, under-floor in unheated cupboards.

Thaw it gently

1. 1

   Turn off the stopcock

   Close the main stopcock so that if the pipe has already split, the thaw doesn't flood you. See our guide on how to turn off your stopcock.

2. 2

   Open the affected tap

   This gives meltwater somewhere to go and means you'll see flow return the moment the ice clears.

3. 3

   Apply gentle heat at the tap end

   Start at the open tap and work back along the pipe. A hairdryer on low, warm towels soaked in hot water, or a thermostat-controlled heat pad are all fine. The ice should melt back towards the cold source.

4. 4

   Keep going until flow returns

   A drip becomes a trickle, then full pressure. Leave the tap running for a minute or two to flush any debris.

5. 5

   Check for leaks

   Once the pipe is thawed and flowing, slowly open the stopcock and walk every length of that pipe. Check ceilings below for damp patches. A split won't always leak immediately.

If the pipe has already burst

You'll know a frozen pipe has split as soon as it starts to thaw — water appears, fast. Shut off the stopcock, open the taps to drain the system, and follow the steps in our first 5 minutes after a burst pipe guide. If you can't stop the flow, call us on the emergency plumber London line — we run 24/7 out of Enfield.

What never to do

• No naked flame. Blowtorches, lighters, paint guns — never.
• No boiling water poured straight on the pipe. Thermal shock can split frozen copper.
• Don't open every tap and walk away. If a pipe has burst upstream, you'll just empty your tank into the ceiling.
• Don't leave it for "later". A frozen pipe that's been thawed once will refreeze the same night — and split the second time.

If you've had a freeze, treat it as a warning shot. Get the pipework properly lagged this side of next winter — it's a cheap job for a plumber and pays for itself the first time it stops a flood. See our burst pipe repair service if you've already had damage.

Frequently Asked Questions

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