What Is a Burst Pipe? Causes, Frozen Pipes and First Steps

Quick answer

A burst pipe is a water supply pipe that has split, cracked open or blown apart at a joint, letting water escape under full house pressure, most often after the water inside froze and the trapped pressure behind the ice became more than the pipe could hold.

Unlike a slow drip, a burst can release large amounts of water quickly. The first response is always the same: shut the main water valve, then call a plumber.

Quick facts

The key facts about Burst Pipe, with sources:

Most common cause: Freezing: ice blocks the pipe and pressure builds in the trapped water ¹²
Water released: An ⅛-inch crack can release up to 250 gallons a day ¹
Pipes most at risk: Near outer walls, in crawlspaces and attics ¹²
Keep heat at: No lower than 55°F during cold snaps or trips ¹³
First step: Shut off water at the main shutoff valve ³
Never: Thaw a pipe with an open flame or torch ¹⁴

Key takeaways

Shut off the main water valve the moment you find a burst pipe, then call a plumber.
Most bursts in cold regions follow freezing; the break is often not where the ice is.
Pipes along outside walls, in crawlspaces and in attics are the most exposed.
Steady heat, insulation and a trickle of water during cold snaps are the main defenses.
Never use a torch to thaw a pipe; Illinois Extension and fire officials both warn against it.

What to do in the first ten minutes

A burst pipe is an emergency. These steps follow utility and extension guidance ³¹²:

Shut the main valve: Turn off water to the house at the main shutoff ³.
Mind the power: If water is near outlets, cords or the panel, stay out of it; Illinois Extension warns of shock risk around standing water ¹.
Open faucets: Leave faucets open to drain the lines until repairs are done, as Phoenix advises ³.
Turn off the water heater supply if the leak is on the hot side.
Call a plumber and your insurance agent ¹².
Document and dry: Take photos, move belongings and start drying.

Water and electricity

Do not step into standing water if it may reach outlets, extension cords or the electrical panel. Shut power only if you can reach the panel from a dry spot; otherwise call your electric utility. Never thaw pipes with a torch or open flame ¹⁴.

Why frozen pipes burst

Frozen pipes burst because an ice plug seals the line and the water trapped behind it, with nowhere to go, is squeezed until the weakest point of the pipe gives way.

The plug forms first where the pipe is coldest, often where it passes an uninsulated rim joist or a gap in a crawlspace vent.

The water between that plug and a closed faucet is then squeezed as more ice forms, which is why a line can split a few feet away from the spot that actually froze.

A University of Illinois summary puts it plainly: an eighth-of-an-inch crack can release up to 250 gallons of water a day, soaking floors, rugs and furniture ¹. The damage often shows only when the ice thaws and water starts flowing again.

This is also why a dripping faucet helps: a slight trickle at night from a faucet on an outside wall, as Illinois Extension advises, gives the trapped water an outlet, so pressure cannot build behind the ice ¹.

The sequence below shows the five stages, and the lesson is that the leak usually appears at the last stage, after the weather warms.

Process From cold snap to burst

Cold reaches pipeOuter wall, attic or crawlspace
Ice plug formsSeals the pipe
Pressure buildsTrapped water between ice and closed tap
Weak point failsSplit or blown joint
ThawWater flows out of the break

Mechanism as described by extension and utility guidance; exact pressures vary. Source: [1] [2]

Types and causes of burst pipes

Type	What happens	Usual setting
Freeze burst	Ice plug traps water; pressure splits the pipe ¹	Exterior walls, attics, crawlspaces, garages
Joint blowout	A fitting separates under stress	Old or poorly made joints; pressure spikes
Corrosion failure	A thinned wall finally gives way	Old galvanized steel or corroded copper
Pressure failure	Pipe or hose fails at high static pressure	Homes with high static pressure and no working pressure-reducing valve
Physical damage	Nail, screw or digging punctures a line	Remodels, yard work

Example: how pipe material handles freezing

Pipe material changes the odds. Two industry design guides report how their pipe behaves when water freezes inside it ⁵⁶.

Pipe	What the guide says	Caveat
Copper, soft (annealed) ½-inch	Withstood freezing as many as 6 times before bursting in testing ⁵	CDA: copper lines should still not be allowed to freeze ⁵
Copper, soft 2-inch	Withstood freezing as many as 11 times in testing ⁵	Same caveat ⁵
PEX	Can expand without cracking and return to size on thawing ⁶	Only with room to expand; in slabs or compacted soil it may be damaged ⁶
Hard copper, CPVC, steel	No freeze-tolerance figure in these sources	Treat as vulnerable

Chart Freeze cycles survived by soft copper tube in testing

In testing reported by the Copper Development Association, water in a half-inch soft copper tube was frozen as many as six times, and in a two-inch tube eleven times, before bursting.

Freeze cycles survived by soft copper tube in testing (freeze cycles before bursting)
Item	Value (freeze cycles before bursting)
½-inch soft copper	6 cycles
2-inch soft copper	11 cycles

Data period: Copper Development Association, Copper Tube Handbook (A4015-26/24), Freezing section

Source: [5]

No pipe is freeze-proof. PPFA says PEX systems should not be intentionally subjected to freezing ⁶, and CDA says the same about copper ⁵. The safe plan is to keep water lines warm.

Where in a house pipes usually burst

Pipes usually burst in the coldest parts of a house, where heat from the living space does not reach. Illinois Extension lists pipes near outer walls, in crawlspaces and in attics, plus pipes inside poorly insulated walls ¹. Add garages, outdoor hose bibbs and sink cabinets on exterior walls.

Warm climates are not exempt. Phoenix’s water department notes the city occasionally freezes and that exposed pipes, especially plastic PVC, are more prone to breaks; it suggests relocating, insulating or covering them ³.

On a plumber’s invoice, burst pipe work may appear as emergency call-out, line repair, section replacement or freeze protection. Our emergency plumbing service covers the call-out.

What acting in the first minutes saves, and what it cannot

Acting within minutes

Shutting the main stops the flow at once ³.
Opening faucets after the main is off drains the lines, which limits how much water escapes through the break.
Early calls to a plumber and insurer, as extension guides advise, speed repair ².
Removing wet rugs and starting fans or dehumidifiers early limits damage to floors, drywall and furniture.

What fast action cannot fix

Pipes that froze may have hidden cracks that leak on thaw.
Water already in walls or ceilings still needs drying.
Thawing a pipe does not repair a split ⁴.
Insurance terms vary; check your policy.

Why thawing a pipe yourself is risky, and the safer heat sources

NC State Extension recommends calling a plumber rather than thawing pipes yourself, because it can cause more damage or be hazardous ². If you do try, work from the open faucet toward the frozen area so steam and water can escape ².

Safe heat sources named by the Dunstable, MA fire department include a hair dryer, an infrared heat lamp, heating cable, or rags soaked in hot water; it says never use a blow torch ⁴. If the pipe has already split, thawing it will only release water. Shut the water off first.

What drives the cost of a burst pipe

We do not publish prices. The bill depends on:

After-hours or holiday emergency call-out.
Where the break is: open basement pipe vs. inside a finished wall or ceiling.
How much pipe must be replaced, and the material.
Water damage: drying, drywall, flooring and mold work.
Whether old pipe suggests repiping rather than another repair.

The leak cost calculator shows how fast water loss adds up, and our cost guide explains quotes.

How a plumber repairs a burst pipe

Isolate: Confirm the main is off and drain the line.
Find every break: Frozen lines can split in more than one place.
Cut out the damage: Remove the split section back to sound pipe.
Replace: Splice in new pipe with approved fittings, often choosing a more freeze-tolerant material.
Test: Restore pressure slowly and check for leaks.
Protect: Add insulation, seal drafts or reroute lines away from exterior walls ¹.

How to keep pipes from freezing and bursting

Insulate pipes in attics, crawlspaces and outer walls with insulation made for pipes ¹².
Use UL-listed heat tape where needed, following its instructions ¹.
Seal leaks that let cold air reach pipes ¹.
Disconnect hoses, close inside valves to outdoor faucets and drain them ³¹.
Open sink cabinet doors and let a faucet trickle on very cold nights ¹.
Keep heat at 55°F or higher, even when away ¹³.

Going away in winter?

Illinois Extension suggests having someone check the heat daily, or draining and shutting off the water system. Phoenix suggests shutting off water to the house and water heater for long trips ¹³.

Warning signs and when to call

No water, or a trickle, from a faucet during a freeze: the line may be frozen ³.
Frost or condensation on an exposed pipe in an unheated space, which means the water inside is close to freezing.
A bulging, cracked or visibly split section of pipe, which should be treated as a leak waiting to happen even if it is dry today.
The sound of running water inside a wall or ceiling while every faucet in the house is closed.
New water stains, sagging drywall or peeling paint on a ceiling or wall after a cold night.

Phoenix advises leaving the faucet on and calling a plumber if nothing comes out ³. Our plumbing emergencies guide covers what to do next.

Freeze-protection codes and pipe standards

Freeze protection: No national rule tells a homeowner how to protect pipes; the model plumbing codes require water pipes exposed to freezing to be protected, but the details and section numbers differ between the IPC, IRC and UPC and with local amendments.

We could not read those sections at source, so we do not quote them. Check the code your jurisdiction adopted.

Pipe standards: PEX water pipe is made to ASTM F876 ⁶; copper tube to ASTM standards and is at least 99.9 percent copper, per CDA ⁵.

Heat tape: Illinois Extension advises UL-approved heat tape ¹; follow the maker’s instructions.

Utility lines: repairs on the private side of the meter are the owner’s job in cities such as Phoenix ³.

Burst pipe vs. related problems

Problem	Speed	Main difference
Burst pipe	Sudden, high flow	Split or blown joint under full pressure
Pinhole leak	Slow drip or spray	Small hole from corrosion
Slab leak	Hidden, often slow	Under a concrete floor
Frozen pipe (not burst)	No flow	Ice blocks the line; may burst on thaw
Water hammer	Bang, no leak	Pressure spike that can weaken joints over time

Burst pipe myths that lead to more damage

Myth Pipes burst where the ice is.: Reality They often split where trapped water pressure finds the weakest point.
Myth PEX cannot be damaged by freezing.: Reality PPFA says it may be damaged if it cannot expand evenly, such as in slabs ⁶.
Myth A torch thaws pipes fastest and safely.: Reality Fire officials say never use a blow torch ⁴.
Myth Warm-climate homes do not need freeze care.: Reality Phoenix tells residents to protect exposed pipes during freezes ³.
Myth Once water flows again, all is fine.: Reality A split may only start leaking once the ice melts.

Climate decides the risk

Freeze risk is set by climate and by where pipes run. In cold states, the danger is pipes in exterior walls, attics and crawlspaces ¹. In mild climates like Phoenix, the risk comes from rare freezes catching exposed outdoor and attic lines unprepared ³. Either way, find your main valve before winter.

When burst-pipe risk should change what you do

Burst-pipe risk matters most before the first hard freeze, whenever a home sits empty in winter, and the moment you see water where it should not be. The guide below matches each of those situations to the step that limits the damage.

Next step: find and test your main water shutoff, insulate exposed pipes, and keep a plumber’s number handy. If a pipe has burst, shut the water off before anything else.

Decision guide What to do in each burst-pipe situation

If Water is spraying or pouring from a pipe: Then Shut the main valve first, stay clear of wet outlets, then call a plumber ³¹
If No water comes out of a faucet during a freeze: Then Leave the faucet open and call a plumber ³
If Pipes run through an attic, crawlspace or outer wall: Then Insulate them and seal drafts before winter ¹
If The house will sit empty in winter: Then Keep heat at 55°F with daily checks, or drain and shut off the water ¹
If The same spot has burst before: Then Ask a plumber about rerouting the line away from the cold wall

Source: [3] [1]

Questions about Burst Pipe

What should I do first if a pipe bursts?

Shut off the water at the main shutoff valve right away. Then stay clear of water near outlets or the electrical panel, open faucets to drain the lines, and call a plumber and your insurance agent. Phoenix’s water department and University of Illinois Extension both give these steps.

Can a frozen pipe thaw on its own without bursting?

Sometimes, but you cannot tell from outside whether it has already cracked. A pipe can split while frozen and only leak once the ice melts, so watch it closely as it warms.

Keep the faucet open, since Phoenix’s water department says to leave it on and call a plumber when nothing comes out. Know where your main valve is in case water appears.

At what temperature do pipes freeze?

Water freezes at 32°F, but pipes freeze based on how cold their spot gets and for how long. Pipes in attics, crawlspaces and outer walls are most at risk. Extension guidance says to keep indoor heat at 55°F or higher during cold snaps and insulate exposed lines.

How much water can a burst pipe leak?

A lot. University of Illinois Extension says an eighth-of-an-inch crack can release up to 250 gallons a day. A full split releases far more. That is why the first step is always to shut the main water valve, even before calling for help.

How do I thaw a frozen pipe safely?

NC State Extension recommends calling a plumber. If you try it yourself, open the faucet and work from it toward the frozen area using a hair dryer, heat lamp or hot wet rags. The Dunstable, MA fire department says never use a blow torch. If the pipe is already split, shut off the water first.

Should I let faucets drip to prevent frozen pipes?

Yes, during hard freezes. Illinois Extension suggests letting water trickle at night from a faucet on an outside wall and opening cabinet doors so heat reaches the pipes. A trickle gives pressure an outlet and keeps water moving. It does not replace insulation.

Does PEX burst when it freezes?

Less often than rigid pipe. The PPFA PEX design guide says PEX can expand without cracking and return to size when it thaws, if it has room to expand evenly. In a slab or compacted soil it may be damaged. PPFA also says PEX should not be intentionally frozen.

Is a burst pipe covered by insurance?

It depends on your policy and the cause. Extension guides advise calling your insurance agent as soon as the water is off. Take photos and keep receipts for emergency repairs and drying. Read your policy for limits on freeze damage in empty or unheated homes.

How do I prevent pipes from bursting when I am away?

Keep the heat at 55°F or higher and ask someone to check it daily, or drain and shut off the water system, as Illinois Extension suggests. Phoenix suggests shutting off water to the house and water heater for long trips. Disconnect hoses and drain outdoor faucets before you go.

Sources

University of Illinois Extension, Cold Weather, Frozen Pipes? Extension Gives You All You Need to Know (February 8, 2021), retrieved October 12, 2026.
NC State Extension, Healthy Homes: Preventing Frozen Pipes, retrieved October 12, 2026.
City of Phoenix Water Services Department, Household Plumbing Tips, retrieved October 12, 2026.
Town of Dunstable, MA Fire Department, Hints for Safely Thawing Frozen Pipes, retrieved October 12, 2026.
Copper Development Association, Copper Tube Handbook (CDA Publication A4015-26/24), retrieved October 12, 2026.
PPI and PPFA (prepared by Home Innovation Research Labs), Design Guide: Residential PEX Water Supply Plumbing Systems, 2nd ed. (November 2013), retrieved October 12, 2026.

Expert review

Written by the HyrePlumber Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.

How the numbers were checked: Emergency steps, at-risk locations, the 250-gallon crack figure and prevention advice are from University of Illinois Extension, NC State Extension and Phoenix Water Services. Thawing safety is from those plus the Dunstable, MA fire department.

Freeze tolerance figures are from two industry guides (CDA for copper, PPI/PPFA for PEX), labeled as such. The freezing mechanism is described generally without pressure figures, because published numbers vary. Code freeze-protection sections were not readable at source and are not quoted. No prices.

Suggest a correction. We fix errors and say what changed.