Turn the water off first, open the tap the pipe feeds, then thaw gently from the tap end back towards the blockage so melt water has somewhere to go. Never use a naked flame. Then insulate or re-route the pipe so it does not happen again.
Before you thaw anything
If the pipe has already split, the ice is plugging it. Thaw it without isolating first and you get a burst running at full mains pressure. Turn the stopcock off before applying any heat, every time.
- Turn the water off at the stopcockNon-negotiable.
- Open the tap that the frozen pipe feedsThis gives melt water somewhere to go and relieves pressure as ice expands. It also shows you progress – a trickle starting means it is working.
- Locate the frozen sectionIt will be in unheated space: a loft above the insulation, a garage, an outbuilding, under a suspended floor, or against an external wall. The pipe is noticeably colder to the touch and is sometimes visibly frosted.
- Work out which end is the tap endYou will thaw from there back towards the blockage.
Thawing
The principle is simple: apply gentle heat starting nearest the open tap and work backwards along the pipe towards the middle of the ice plug. That way, as ice melts, the water has an open route out rather than being trapped between two plugs.
- A hairdryer on a low or medium setting, moved continuously along the pipe. The most common and most controllable method.
- Towels soaked in hot water, wrapped around the pipe and replaced as they cool. Slow, gentle and very safe.
- A hot water bottle laid along the pipe.
- A heat mat or trace heating, if you have it.
- Warming the space, which helps everything and is worth doing alongside whichever method you use.
Expect it to take time. A well-frozen pipe in a cold loft is not going to thaw in three minutes, and rushing is what causes damage.
What never to use
- A blowtorch or any naked flame. Beyond the obvious fire risk in a loft full of insulation and dry timber, localised intense heat turns trapped water instantly to steam, and steam in a closed section of pipe bursts it violently.
- A heat gun on high. Same problem, less obviously.
- Boiling water poured over the pipe. Thermal shock on cold metal or plastic can crack fittings, and on a genuinely cold day it refreezes into a larger blockage.
- Heating the middle of the run first, which traps melt water between two ice plugs with nowhere to go.
As it thaws
- Watch every joint. Compression fittings are pushed apart by expanding ice and frequently start weeping as they thaw. Soldered joints can fail too.
- Watch the pipe itself for splits – a longitudinal split along the pipe is the classic frost failure.
- Listen. Running water where there should not be any is the first sign.
- Be there when you turn the supply back on. Turn it on slowly and stay with it for several minutes. If something has split, you want to be standing next to the stopcock.
- Check the affected area again a few hours later, and again the next morning. Slow weeps take time to show.
Why that pipe froze
A pipe freezes where there is no heat, moving air and inadequate insulation. Knowing which of those applies tells you how to fix it.
| Situation | Why it froze | Fix |
|---|---|---|
| Loft pipe above the insulation | Modern loft insulation is thick, so the loft is genuinely cold now | Run it below the insulation, or lag it thoroughly and continuously |
| Pipe in an unheated garage or outbuilding | No heat at all | Lag, or fit a drain point and empty it in autumn |
| Pipe against an external solid wall | No cavity, no insulation | Insulate, or re-route |
| Pipe in a draught path | Moving cold air. The real culprit more often than temperature | Seal the draught – eaves, service penetrations, loft hatch |
| External run to an outside tap | It is outside | Isolation valve and drain point, emptied each autumn |
| Condensate pipe | Small bore, permanently wet | See frozen condensate pipes |
A lagged pipe in still cold air usually survives a normal cold snap. The same pipe with cold air moving over it does not. Sealing the draught into a loft is frequently more effective than adding more lagging.
Preventing it properly
- Lag every pipe in unheated space, continuously. The gaps at bends, valves and tees are where pipes actually freeze, and they are exactly the places lagging is usually missing.
- Put loft pipes below the insulation where possible, so they sit on the warm side of the thermal envelope.
- Insulate the cold water tank, but not underneath it – heat rising from the house below is what keeps it above freezing.
- Seal draughts into the loft.
- Fit isolation and a drain point on every external run, and empty them in autumn.
- Keep the heating on a frost setting when away in winter. Turning everything off for a fortnight in January is how empty properties get destroyed.
- Drain down properly for long absences, which means draining rather than just switching off.
- Leave internal doors open in a cold snap to let warmth reach cold corners.
- Let a tap drip during exceptional cold, as a short-term measure – moving water freezes far less readily.
Had a pipe freeze this winter? Autumn is when to deal with it. The same pipe will freeze again in the same conditions.
Questions we get asked about this
Can I use a blowtorch on a frozen pipe?
No. Fire risk in a loft, and localised intense heat turns trapped water to steam which bursts the pipe. A hairdryer or hot towels, patiently.
Should I turn the water off before thawing?
Yes, always. If the pipe has split, the ice is the only thing holding the water back and thawing without isolating gives you a burst at full pressure.
How do I know if it has burst?
You often will not until it thaws. Watch every joint and the pipe itself as it melts, turn the supply back on slowly, and stay with it for several minutes.
How long does it take to thaw?
Anywhere from minutes to hours depending on how much pipe is frozen and how cold the space is. Patience is safer than speed.
Should I leave the taps dripping in cold weather?
During an exceptional cold snap it genuinely helps – moving water is much less likely to freeze and a dripping tap relieves pressure build-up. It is a stopgap, not a substitute for insulation.
My house will be empty over winter. What should I do?
Either leave the heating on a frost setting with somebody checking it, or drain the system down properly. Turning everything off and walking away is how empty properties get wrecked.
Need this doing?
Call and describe the problem — you will speak to an engineer, not a call centre. Written quotes, no estimates over the phone.