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Frozen Pipes
A tap has stopped running in cold weather, or a pipe in the loft or garage is iced up.
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What's happening?
Water expands as it freezes, and a pipe full of ice has nowhere to put that expansion, so it splits. The dangerous part is that a frozen pipe usually looks fine — it is only when it thaws and the ice plug clears that water pours out of the split. Freezing happens where pipework is outside the heated envelope: lofts above the insulation, unheated garages, outbuildings, and runs against or through an outside wall. The first sign is almost always an outlet that has stopped: a bathroom tap dry while the kitchen still runs, or a loft tank that stops filling.
What usually causes it?
- Unlagged pipework in a loft, sitting above the insulation in the cold rather than below it
- Pipes in an unheated garage, outbuilding or under a suspended floor with open airbricks
- Loft insulation laid over the tank as well as the joists, cutting the tank off from house warmth
- An outside tap left connected without an isolating valve closed and the tap drained
- A property left unheated during a cold snap while empty
- Pipework run through an external wall cavity or clipped to cold brickwork
- A boiler condensate pipe run externally, which freezes and shuts the boiler down
Is it dangerous?
The freeze is not the danger; the thaw is. A pipe that split while frozen releases water the moment the ice clears, often when nobody is watching, and mains-fed pipework will keep releasing it until the stop tap is closed. Never thaw a pipe with a blowtorch or any naked flame — that is a fire risk in a loft full of insulation and timber, and heating one spot fast can burst the pipe outright.
Can I fix it myself?
Close the internal stop tap first, so that if the pipe has already split you are not standing under it when it thaws. Open the affected tap so meltwater has somewhere to go, then apply gentle heat to the frozen section from the tap end backwards: a hot water bottle, warm damp towels, or a hairdryer on a low setting kept moving. Work slowly. If the pipe is out of reach, buried, or you cannot find the frozen section, leave it and get help. Keep the heating on low rather than off while the cold weather lasts.
When should you call a plumber?
Call a plumber if you cannot reach or locate the frozen section, if water appears as it thaws, or if the pipe serves a system you cannot isolate. Call before the thaw if the property has been empty and unheated through a hard freeze — it is far cheaper to check and repair a split under control than to find it by walking into a flooded room. A frozen external boiler condensate pipe is a heating engineer's job rather than a plumber's.
What will the plumber actually do?
- Isolate and drain the affected section before thawing so a hidden split cannot flood the house
- Thaw the run under control and inspect the whole length for splits and strained joints
- Cut out and replace any split pipe, and remake joints that have been stressed
- Pressure-test and refill, then check every outlet on the run
- Lag exposed pipework and re-position insulation so loft tanks and pipes sit within the warm zone
- Fit a drain-down point or an isolating valve for an outside tap so it can be emptied each autumn
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