Frozen Pipes: Preventing Them and Thawing Them Safely
A frozen pipe is a problem twice over: once when the water stops, and again when the ice expands and splits the pipe so that the real damage arrives on the thaw.
A frozen pipe is a problem twice over: once when the water stops, and again when the ice expands and splits the pipe so that the real damage arrives on the thaw. Almost all of it is preventable with insulation, sensible heating settings and a bit of preparation before the first hard frost, and the pipes at risk are entirely predictable — anything in a loft, a garage, an outbuilding, an external wall or an unheated void.
Which pipes freeze and why
Water freezes where it is still and cold. That means pipework in unheated lofts, garages, outbuildings and crawl spaces, external taps and their supply, condensate pipes run outside, and any pipe against an uninsulated external wall. Modern loft insulation makes this worse, not better, because the loft is now colder than it used to be while the pipes above the insulation are just as exposed. Pipes that are used regularly rarely freeze; the ones that catch people out are the ones nobody draws water through in winter.
Insulation done properly
Lagging needs to fit the pipe diameter, be continuous, and cover bends, valves and joints rather than stopping short of them, because those gaps are exactly where freezing starts. Never insulate above loft pipework and leave it exposed to the cold below — insulate the pipes themselves and leave the loft insulation gap under any tank so warmth from the house can reach it. Outside taps need an isolating valve indoors so the external section can be drained before winter.
Condensate pipes: the winter classic
A condensate pipe carries acidic water away from a condensing boiler, and if it runs outside in small-bore plastic it can freeze and lock the boiler out on the coldest morning of the year. Prevention is proper insulation, a larger-diameter external run, or ideally re-routing it internally to a soil stack or waste. Where it does freeze, warm — not boiling — water poured over the exposed pipe usually clears it, after which the boiler can be reset.
Heating settings while you are away
Turning the heating off entirely to save money while away in winter is a false economy. A low background setting, or a frost protection setting where the controls offer it, costs very little and keeps pipework above freezing. Leave internal doors and loft hatches ajar so warmth reaches cold corners, and ask someone to check the property if it will be empty for more than a few days.
Thawing a frozen pipe without causing damage
Turn off the stopcock first, so that if the pipe has already split you are not simply waiting for it to flood on the thaw. Apply gentle heat starting at the end nearest the tap and working back — warm cloths, a hairdryer on low, or warm water. Never use a blowtorch or any naked flame, and never use boiling water on plastic. Open the tap so melting water has somewhere to go, and watch carefully for leaks as the section clears.
The pre-winter checklist
Late autumn is the time: lag exposed pipework, drain and isolate outside taps, check the loft hatch and any tank insulation, confirm the stopcock turns freely, service the boiler so it goes into winter healthy, and make sure whoever else lives in the property knows where the stopcock is. Every one of those is cheap compared with a single burst pipe in a loft over Christmas.
Before the first hard frost
- Lag all loft, garage and outbuilding pipework
- Cover bends, valves and joints, not just straight runs
- Isolate and drain outside taps
- Insulate or re-route the external condensate pipe
- Check the stopcock turns freely
- Set a low background heat rather than switching off
- Leave the loft hatch ajar in very cold spells
- Have the boiler serviced before winter
Who does the work
- Gas Safe registered engineers — registration 554328
- Worcester Bosch accredited installer
- John The Plumb Ltd, company registration 10026483
Get your pipework protected before winter
Tell us where your exposed pipework runs and we will get it lagged, drained or re-routed before the cold arrives.
Questions we get asked
Can I pour boiling water on a frozen pipe?
No. Boiling water can crack the pipe or fitting through thermal shock, and it is dangerous on plastic. Use warm water or gentle heat.
How do I know if a frozen pipe has split?
You often will not until it thaws. That is why the stopcock goes off before thawing begins, so any split leaks into a pipe you have already isolated.
Why does my boiler lock out only on freezing mornings?
Almost always a frozen condensate pipe. Thawing the external section and resetting usually restores it, but the pipe should be insulated or re-routed to stop it recurring.
Should I leave taps dripping in cold weather?
A very slight flow can help on a pipe known to be at risk, but proper insulation is a far better answer than running water away all night.
What heating setting should I leave on while away?
A low continuous background temperature or the controls' frost setting. Off is the setting that causes burst pipes.