The short answer
Pipes freeze when water inside them turns to ice and expands, building pressure that can crack the pipe. Thaw a frozen pipe gently, never with a naked flame. If one bursts, turn off the stop tap, switch off your heating, open the taps to drain the system, and keep water away from electrics.
A cold snap is one of the few times a quiet, well-behaved plumbing system can turn on you overnight. Water that has sat happily in your pipes for years freezes solid, and a few hours later you have a split copper pipe and a soaked ceiling. The frustrating part is that the damage often does not show itself until the thaw, by which point the water has had a head start. Knowing what to do, in order, makes the difference between a dried-out cupboard and weeks of repair work.
This guide walks through why pipes freeze and burst, how to thaw one safely, the steps to take if a pipe has already gone, how a hidden or underground burst is tracked down, and a few simple habits that stop the whole thing happening in the first place.
Why pipes freeze and burst
Water is unusual in that it expands as it freezes. As it turns to ice it takes up roughly nine per cent more space, and inside a sealed pipe that extra volume has nowhere to go. Pressure builds, and it does not always build at the frozen plug itself. Often the ice forms a blockage, water backs up behind it, and the pressure is forced against a weaker section further along the run. That is the point that splits.
Because of this, the actual crack can be some distance from where the pipe is frozen. It also explains why a burst so often reveals itself only when things warm up. While the ice is in place it acts as its own plug. As soon as the surrounding temperature rises and the ice melts, water starts flowing through the split, and that is when the leak appears.
The pipes most at risk are the ones running through cold, unheated spaces or against external walls: lofts, garages, outbuildings, and the runs to outside taps. Repeated freezing and thawing over several winters also wears at the metal, so a pipe that has coped before is not guaranteed to cope again.
Signs a pipe may be frozen:
- No water, or only a trickle, when you open a tap in cold weather
- Frost or condensation visible on an exposed pipe
- Gurgling or banging sounds when you try to run water
- A bulge or unusual shape in a section of pipe
- Damp or staining nearby once a thaw begins
How to thaw a frozen pipe safely
If you find a frozen pipe before it has burst, you can often thaw it yourself, provided you go slowly and resist the urge to rush it with strong heat. The single most important rule is never to use a naked flame. A blowtorch or any open flame can damage the pipe, scorch nearby materials, and create a real fire risk. Sudden, intense heat can also make a weakened pipe fail on the spot.
Before you start, open the cold tap nearest the frozen section and leave the stop tap turned off. The open tap gives any meltwater somewhere to go and helps relieve pressure as the ice clears. Then apply gentle warmth to the frozen part of the pipe. Good options include a hot water bottle held against it, towels soaked in warm water and wrapped around it, or a hairdryer on a low setting.
Work from the tap end back towards the frozen blockage rather than starting in the middle. This lets the melting ice and water escape through the open tap instead of being trapped behind a section that is still solid. If you use a hairdryer, keep it moving and never leave it resting in one spot. Take your time. A pipe that thaws gently is far less likely to split than one forced open in a hurry, and as it clears you will see the flow at the tap return to normal.
What to do if a pipe has burst
If a pipe has already burst, acting quickly limits the damage. The first job is to stop the water. Turn off the stop tap, which is usually found under the kitchen sink, in an airing cupboard, or near where the mains enters the house. It is worth knowing where yours is before you ever need it, because hunting for it while water pours through a ceiling is nobody’s idea of fun.
With the stop tap off, switch off your boiler or central heating system, then open all the taps in the house to drain the remaining water out of the pipes. Catching some water in a bucket or two is sensible, as it can be used for flushing the loo and washing your hands while the supply is off. Soak up escaping water with towels to keep it from spreading into floors and skirting boards.
Electrics deserve particular caution. Water and electricity are a dangerous mix, so if water is anywhere near light fittings, sockets, or your consumer unit, do not touch them. If you have any doubt at all about the safety of the electrics, keep clear of the affected area and have them checked by a qualified electrician. Once the water is off and contained, it is time to get a leak found and the pipe repaired.
Finding a hidden or underground burst
A burst in plain sight is straightforward enough. The harder ones are the pipes you cannot see, running under floors, behind walls, or buried in the ground on the way to an outside tap or supply. Here the split may not announce itself with a dramatic flood at all. Instead you get the quieter clues: a damp patch creeping across a ceiling or wall, bubbling paint or plaster, a musty smell, or a soft, soggy area of lawn that stays wet when everywhere else has dried.
Other signs are worth watching for too. An unexplained jump in your water bill often points to water escaping somewhere out of view, and even a small crack can lose a surprising amount over a day. A simple meter check can help confirm it: with every tap and water-using appliance switched off, note your meter reading, leave it an hour without using any water, then read it again. If the numbers have moved, water is going somewhere it should not. For matters relating to your supply or meter, your water company, South West Water, is the right first point of contact.
Pinpointing the exact spot without digging up the whole garden or lifting every floorboard is where specialist equipment earns its place. Acoustic listening devices pick up the faint sound of water escaping under pressure, while thermal imaging can reveal the temperature change a leak leaves behind on a floor or wall. Used together, these methods locate the problem precisely, so the repair can be targeted rather than guessed at. Our water leak detection service uses exactly this kind of non-invasive approach across Devon, with same-week appointments often available.
Preventing frozen pipes
A little preparation before winter sets in goes a long way. The most effective single step is lagging, which means fitting foam insulation sleeves over exposed pipes so the cold cannot get to the water inside. Pay particular attention to the pipes in lofts, garages, and outbuildings, and to the runs feeding outside taps, as these are the ones that suffer first. Lagging is inexpensive, sold in most DIY shops, and quick to fit.
Beyond insulation, keeping the house gently warm during a cold spell helps, even when you are out, rather than letting the temperature drop right off. Knowing where your stop tap is, and checking that it actually turns, means you can react fast if the worst happens. If you are going away during freezing weather, leaving the heating ticking over on a low setting, or draining the system down entirely, removes the risk of returning to a flood. None of these steps is difficult, and together they make a burst far less likely.
Frequently Asked Questions
Water freezes at zero degrees Celsius, but a pipe needs to stay at or below that for a sustained period before the water inside turns to ice. Pipes in exposed, unheated spots such as lofts and garages reach freezing faster than those kept within a warm house, which is why they tend to be the first to go.
While a pipe is frozen, the ice acts as its own plug and holds the water back, so a split may not leak at all. As the ice melts and water starts flowing again, it escapes through the crack. This is why many bursts are not discovered until a thaw is well under way.
No. A naked flame should never be used on a pipe. It can damage the pipe, set fire to nearby materials, and cause a weakened section to fail. Stick to gentle heat from a hot water bottle, warm towels, or a hairdryer on a low setting, working from the tap end back towards the blockage.
In most homes the internal stop tap is under the kitchen sink, in an airing cupboard, or close to where the mains supply enters the property. It is worth locating it and checking it turns freely before winter, so you can shut the water off quickly if a pipe bursts.
Specialist leak detection uses non-invasive tools such as acoustic listening equipment, which hears water escaping under pressure, and thermal imaging, which shows the temperature change a leak leaves on a surface. These methods pinpoint the spot so the repair can be focused on one area rather than the whole floor or wall.
We provide leak detection across Devon, with same-week appointments often available. If you suspect a frozen or burst pipe and need the leak located, get in touch on 07897 027775 and we will arrange a visit where possible.
Worried About a Frozen or Burst Pipe?
If a pipe has gone, or you have spotted damp that will not dry out, we can locate the leak quickly and without tearing your home apart. Get in touch and we will help you sort it.