A pipe froze: what do you do first?

The first ninety seconds

Go to the main shut-off before you touch the frozen pipe. In a basement it is usually near where the supply enters the wall; in a slab house it is often in a garage or a utility closet; outside, it is at the meter and may need a key. Turn it far enough to know it moves, then leave it in the open position. The single worst outcome of a freeze is discovering, while water is spraying, that you do not know where the valve is or that it is seized.

Then open the faucet the frozen line feeds, both handles if it has two. An open faucet gives the ice somewhere to expand toward as it melts and tells you the instant flow returns.

Warming the pipe without making it worse

Work from the faucet end back toward the frozen section, never the other way. Warming the middle of a plug first traps meltwater between two ice masses and builds pressure exactly where you do not want it.

A hair dryer on a low setting, a heat gun kept moving, an electric space heater positioned to warm the cavity, or towels soaked in hot water wrapped around the pipe are all fine. What is not fine is any open flame, and that includes propane torches, which start structure fires in wall cavities every winter, and it includes leaving a heater unattended against wood framing. If the pipe is plastic, a torch is also destroying it directly.

Opening a cabinet door under a sink on an exterior wall so room air can reach the pipes is a small thing that works, both now and as prevention.

When to stop and call

Stop and call a plumber if any of these is true. You cannot identify where the frozen section is. The line runs inside a finished wall, ceiling, or under a slab. You can see a bulge, a split, or a green or white crust that suggests a slow leak that has been going on. More than one fixture has lost water, which suggests the freeze is on a main rather than a branch. Or the house has been unheated and you do not know what condition the whole system is in.

Close the main first, then call. A split pipe upstream of a closed valve is an inconvenience. A split pipe with the water on is a flood.

After it thaws

Watch the repaired or thawed area for a full day. Copper that has been frozen can split in a way that only leaks under full pressure and only once the ice is fully gone, so the water often appears hours after the crisis felt over. Check the ceiling below and the floor around it.

If water did escape, the clock that matters is a short one. Wet building materials start growing mould within a couple of days, and the difference between drying an area promptly and dealing with it a week later is a different scale of work entirely.

Preventing the next one

The pipes that freeze are the ones in unconditioned space: crawl spaces, attics, garages, exterior walls, and hose bibs. Insulating those runs is cheap. Draining and disconnecting garden hoses in autumn prevents the most common single failure in mild climates, because a connected hose keeps water sitting in the bib where it freezes and splits behind the wall. Sealing the air leaks that let cold air reach a pipe usually helps more than the insulation itself, since insulation slows heat loss but does nothing about a direct draught.

In a genuine cold snap, letting a single faucet on the most vulnerable run drip is a reasonable, low-cost insurance policy. Moving water is much harder to freeze than still water.

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