A frozen pipe should be thawed gently from the tap end back towards the blockage, never with a naked flame. The pipes that freeze are those in unheated space, and once one has frozen it will freeze again in the same conditions unless it is insulated or re-routed.
If a pipe is frozen right now
- Turn the stopcock offIf the pipe has split, the ice is currently the only thing holding the water back. Isolating first means the thaw does not become a flood.
- Open the tap that the frozen pipe feedsThis gives the melting water somewhere to go and lets you see progress. It also relieves pressure as the ice expands.
- Find the frozen sectionIt is in unheated space – a loft, garage, outbuilding, under a suspended floor, or against an external wall. Often you can feel it: the pipe is noticeably colder and sometimes frosted.
- Thaw gently, starting at the tap endWork back towards the blockage so the melt water has somewhere to escape. A hairdryer on low, warm towels, or a hot water bottle laid on the pipe. It takes patience.
- Check every joint as it thawsWatch for weeping or splits. Compression joints in particular get pushed apart by ice.
- Turn the water back on slowlyAnd stay with it. If something has split, you want to be there when it starts.
No blowtorch, no heat gun on high, no naked flame of any kind. Beyond the obvious fire risk in a loft full of insulation, rapid localised heating turns trapped water to steam and can burst the pipe violently. Do not thaw the whole run at once from the middle either – trapped melt water between two ice plugs has nowhere to go.
Which pipes freeze, and why
Pipes freeze where there is no heat, moving air, and no insulation. In Norfolk housing that means a predictable list:
- Loft pipework laid on top of the insulation. Modern loft insulation is thick and effective, which means the loft is now colder than it used to be. A pipe run over the top of it sits in outdoor temperatures. Run below the insulation where possible; lagged thoroughly where not.
- Cold water storage tanks in the loft, particularly the ball valve and the short exposed runs around it.
- Garages and outbuildings, especially detached ones with no heat at all.
- Pipes against external walls, in older properties with solid walls and no cavity.
- External runs to outside taps and outbuildings, which should be drainable – see outside taps.
- Condensate pipes from condensing boilers, which are a special case because they are permanently wet and small bore.
- Anywhere a draught blows, which is often the real culprit. A pipe in a cold but still space usually survives; the same pipe with cold air moving over it does not.
Frozen condensate pipes
This deserves its own explanation, because it is by far the most common cold-weather call and it is usually not a burst at all.
Every condensing boiler – gas or oil – produces acidic condensate that must drain away. If the condensate pipe runs outside and the temperature drops, it freezes. The boiler detects that it cannot drain, and shuts itself down. Many boilers display a specific fault code for it. There is nothing broken: the boiler is protecting itself.
The immediate fix is to thaw the pipe, usually by pouring warm – not boiling – water over the external section, or holding a hot water bottle against it, then resetting the boiler. The permanent fix is to reroute the condensate internally, or where that genuinely is not possible, to increase the pipe diameter, insulate it properly, shorten the external run and improve the fall. There is more detail in frozen condensate pipes.
Preventing it properly
The preventive work is cheap, and it is the only thing that changes the outcome next winter.
| Measure | Why it works |
|---|---|
| Lag every pipe in unheated space | Slows heat loss enough that a pipe survives a normal cold snap. Must be continuous – the gaps at bends, valves and tees are where pipes actually freeze |
| Run loft pipes below the insulation | Puts them on the warm side of the thermal envelope rather than the cold side |
| Insulate the cold tank but not beneath it | Lets heat from the house below keep the tank above freezing |
| Seal draughts into the loft | Moving cold air is what does the damage. Still cold air rarely freezes a lagged pipe |
| Fit drain points on external runs | Empty it in autumn and there is nothing to freeze |
| Keep the heating on low when away | A frost setting costs very little against a burst. Never turn it off entirely for weeks in winter |
| Drain down properly for long absences | The right answer for a property standing empty over winter – and it means draining, not just turning off |
Had a pipe freeze this winter? Autumn is when to deal with it, not the next cold snap.
Questions we get asked about this
How do I know if a frozen pipe has burst?
You often will not until it thaws, because the ice is blocking the split. Turn the water off before thawing, watch every joint as it melts, and stay with it when you turn the supply back on.
Can I use boiling water on a frozen pipe?
Warm water is fine and effective on an external condensate pipe. Boiling water is not a good idea on a metal pipe – the thermal shock can crack fittings, and on a very cold day it simply refreezes into a worse blockage. Warm, patient and repeated works better.
My boiler has shut down in cold weather. Is it broken?
Probably not. A condensing boiler that shuts down during a freeze is very often a frozen condensate pipe, and it will restart once thawed. Check the fault code and look at the external plastic pipe from the boiler before assuming the worst.
What temperature do pipes freeze at?
Water freezes at zero, but a pipe in a sheltered position can survive a few degrees below that for hours. What matters is duration and wind. Two or three days of sustained sub-zero weather, especially with a draught, is what actually freezes domestic pipework.
Should I leave taps dripping in cold weather?
It genuinely helps as a short-term measure, because moving water freezes far less readily than still water, and a dripping tap also relieves pressure build-up. It is a stopgap during an exceptional cold snap, not a substitute for insulation.
My house is empty over winter. What should I do?
Either leave the heating on a frost setting and ask someone to check it, or drain the system down properly. The middle option – turning everything off and walking away – is how empty properties get destroyed, and it is what we get called to every January.
What happens when you call
Call and describe it
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Certificates where the work needs them, and what will need attention next.
Where we do this work
Across Norwich and the whole of Norfolk. If you are on the edge of the county, call and ask — we will tell you honestly whether we are the right people.
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Need this doing?
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