Frozen Pipe: How to Thaw It Safely and Prevent It from Bursting

If a faucet runs slowly or not at all during a hard freeze, most likely a section of the plumbing — an exposed stretch, an outdoor connection, or even the buried line entering the house — has frozen. The safe approach is gradual, controlled heating, applied from the faucet toward the blockage, with the faucet left slightly open while the ice melts. An open flame has no place near a pipe, because PPR plastic becomes brittle in the cold and can be irreversibly damaged if exposed to excessive, concentrated heat. Once the water starts flowing again, an equally important step follows: carefully inspect the pipe run, because a crack caused by ice expansion may only become apparent once the pressure returns to normal.

• Open the faucet slightly before you start heating, so you can see as soon as the water starts flowing again and reduce the risk of pressure remaining trapped in the pipe.
• Heat gradually, from the faucet toward the frozen spot, using controlled heat sources — a hair dryer, a warm towel, an electric heating pad — and never an open flame.
• After thawing, monitor the flow and inspect the visible pipe run for damp patches or leaks, even if the water seems to have returned to normal.
• If the blockage is inaccessible, you’re unsure what the pipe is made of, or you see any sign of a leak, stop and call a licensed plumber.

Why pipes freeze and what can actually burst

Water behaves differently from most liquids when it freezes: instead of shrinking in volume, it expands. This expansion is what can put stress on a pipe wall and eventually crack it (source: Pipe insulation, Wikipedia) — it’s not the cold itself, but the pressure the ice exerts from the inside out. At temperatures below 0°C, the polypropylene used in most PPR pipes becomes brittle (source: Polypropylene, Wikipedia), so while the pipe is frozen, it is especially vulnerable to mechanical shocks or sudden handling, such as hitting it to check whether it has already burst.

What cold actually does to a PPR pipe

The main risk is not that the cold melts or weakens the material, but that it makes it less elastic just as internal pressure rises because of ice formation. At the other extreme, the same polypropylene has a melting point of approximately 160–166°C and begins to break down structurally with sustained exposure above 100°C (source: Polypropylene, Wikipedia) — a concrete reason why very powerful heat sources, or sources applied directly to the same spot without moving, can weaken the pipe just as effectively as severe cold, only through a different mechanism. A thin section containing a small volume of water reaches freezing temperature faster than a thick pipe, which is why exposed connections and outdoor risers are usually affected first.

Why a buried pipe can freeze even though it’s underground

The fact that a pipe is underground does not automatically mean it’s protected from freezing weather. Water pipes are generally buried below the frost depth — the layer to which the ground is expected to freeze during a typical winter — specifically to keep the cold from reaching them. However, this depth varies widely depending on the climate and soil type, from less than half a metre to nearly two metres, depending on the region (source: Frost line, Wikipedia).

A section buried less deeply than it should be, a connection left exposed near the house foundation, or a layer of soil later reduced by excavation or erosion can leave the pipe closer to the cold than originally intended. Additional insulation — foam or heat tape — does not prevent still water in a pipe from freezing; it only delays when it happens. That’s why it is usually combined with a heating cable or a way to maintain a constant flow of water (source: Pipe insulation, Wikipedia). In practice, an unusually long or cold winter can freeze a line that had weathered previous years without any problems, even if nothing about the plumbing has changed.

Safe steps for thawing a pipe

Leave the faucet slightly open before starting any heating, so you can see as soon as the water starts flowing again and reduce the risk of pressure created by the gradual melting of the ice becoming trapped between the blockage and the faucet.

Then apply heat gradually, starting at the end closest to the faucet and moving toward the frozen spot, not the other way around — otherwise, the melted water has nowhere to drain and may remain trapped exactly where the pressure is already higher.

Good heat sources include a hair dryer kept moving, an electric heating pad or blanket wrapped around the pipe, towels soaked in warm (not hot) water and refreshed periodically, or warm air from a portable heater kept at a distance from the material. The common principle is movement and gradual heating: no heat source should remain stationary on the same spot for minutes at a time.

What you should never do

Never use an open flame — a lighter, torch, or propane burner — near a pipe, regardless of its material. Besides the fire risk, such concentrated heat can quickly exceed the point at which polypropylene begins to break down structurally, even if the surface does not look damaged at first. Also avoid hitting the pipe or forcing the faucet or connection to check whether it has already burst: a material made brittle by the cold is more likely to crack when subjected to a mechanical shock.

What to check after the pipe has thawed

Once the water is flowing again, focus on pressure and flow: if the reopened faucet produces a visibly weaker stream than usual, that could mean there’s a crack farther along the pipe run, not just ice still somewhere in the pipe.

It’s also worth visually checking the accessible pipe run — under the sink, in the basement, or along the wall where the pipe runs — for damp patches, drips, or the sound of running water when no faucet is open.

For a section buried underground or hidden in a wall, a damp patch that appears only hours or days after thawing is a typical sign: the crack caused by ice expansion may only have opened fully once normal pressure returned to the pipe, not at the moment it froze.

When to call a plumber instead of carrying on by yourself

Three situations call for a licensed plumber rather than carrying on by yourself. First: you can’t find the exact location of the blockage, or it is in a buried or walled-in section that cannot be accessed without breaking something open — trying to heat a long stretch of pipe “at random” increases the risk of damaging the material without necessarily solving the problem. Second: after thawing, you see a leak, a patch that spreads from one hour to the next, or the pressure remains unusually low — signs that the issue is no longer “just frozen” and now concerns the integrity of the plumbing. Third: you’re unsure what the pipe or connection is made of, or you don’t know the pipe’s diameter and age — details that affect which heat sources are suitable. Without them, any further testing becomes an unnecessary risk.

What an automatic shut-off leak detector can do after a freeze

The scenario described above — a crack caused by freezing that only shows up once the water starts flowing again — is exactly where an automatic shut-off leak detector on the main water line makes a difference. The ultrasonic sensor mounted on the main line continuously monitors the flow, with a stated sensitivity of up to 0.01 GPM, enough to detect a leak well below the threshold you would notice by watching the faucet yourself. When the flow exceeds the home’s usual parameters, the motorized valve automatically shuts off the water supply within seconds, and the Smart Life app sends an alert.

It’s worth being clear about what this kind of device changes and what remains beyond its capabilities: no sensor mounted on a pipe can prevent the pipe itself from freezing, and having one does not guarantee that no damage will occur. Its role is more specific: it limits the amount of water lost between the moment a crack formed during freezing actually opens and the moment you notice the problem — the difference between a damp patch and a flood discovered only after you’ve been away from home for several days.

For preparation before the cold season, with practical steps for insulation and draining, see our dedicated guide: how to prevent pipes from freezing before it becomes a problem. If the pipe has not only frozen but already burst, and you need immediate steps for the first few minutes, see what to do immediately after a pipe bursts. If a buried line keeps causing problems and you want to pinpoint the leak outside the house, the dedicated article explains how to find a leak in a buried pipe. And for the full picture of leak detectors and automatic shut-off valves, our dedicated guide to smart automatic shut-off leak detectors describes other situations where they’re useful, not just freezing-related ones.

Frequently asked questions

How long can a pipe stay frozen without bursting?
There’s no set time: it depends on how full the pipe is with standing water, the outdoor temperature, and how well that section is insulated or protected. The longer the ice remains and the more internal pressure rises, the greater the risk of cracking. So controlled thawing as soon as you notice the problem is safer than waiting to see what happens.

Can I use a hair dryer on a PPR pipe without damaging it?
Yes. Kept moving and at a reasonable distance, an ordinary hair dryer does not reach the temperatures at which polypropylene starts to break down structurally. The problem arises if you hold it in one place for minutes at a time, at maximum power — it can concentrate enough heat in that spot to damage the material, even without a flame.

What should I do if I can’t find the exact spot where the pipe froze?
If you’ve already heated the accessible section from the faucet and the water still isn’t flowing, the blockage is probably farther along the pipe run, in an underground or walled-in area. In this case, continuing “at random” is no longer a safe solution, and the next step is to call a plumber who can locate the problem without risking the integrity of the plumbing.

Why did a buried pipe freeze if it’s underground?
Because the burial depth is designed for a typical winter in that area, not every possible scenario. A shallower section, an exposed connection, or an unusually long winter can bring the cold closer to the pipe than originally anticipated, as explained above.