What to Do When Underground Water Pipes Are Frozen

Is Your Underground Pipe Frozen or Burst?

A frozen line shows no water or just a trickle at every faucet, with no pooling anywhere. A burst line shows pooling water, a constant running sound, or active leaking. This can happen within hours of severe cold, or only after the line has stayed frozen for days, according to Ostrom Services.

This guide covers the buried service line between the street and your house, not the exposed pipes inside your walls. Interior pipes are usually easier to reach and thaw faster.

No water or a trickle at every fixture means ice is blocking the line completely. A partial blockage can show up first as low pressure at just one or two fixtures, an early warning worth acting on before the line fully seals shut.

If you see pooling water or active leaking, treat it as already burst. Locate your main water shutoff valve and turn it off, then call a plumber. For what to expect next, see what happens when frozen pipes burst.

Why Do Underground Pipes Burst When Frozen?

Freezing water expands and forms an ice blockage that acts like a dam inside the pipe. Pressure builds between the ice and the open faucet until the pipe wall ruptures, often far from where the ice actually formed.

The crack can stay sealed by the ice itself at first, so nothing leaks yet. Once the ice melts and water starts flowing again, it rushes through the break and floods the area. That is why damage sometimes shows up hours or days after a cold snap ends.

1. Water in the pipe cools below 32F and begins forming ice.
2. The ice crystal grows into a blockage that plugs the line.
3. Water pressure builds between the blockage and the open faucet.
4. The pipe wall weakens and small cracks begin to form.
5. The pipe fails, usually away from where the ice sits.
6. The ice may seal the crack for now, so nothing leaks yet.
7. Once the ice fully melts, water rushes through the break.

This delayed pattern is also why a line that seems fine right after a freeze can still flood your yard or basement once the weather warms back up.

How Fast Do Underground Pipes Freeze?

Freeze speed depends on temperature and insulation, not just the 32F freezing point of water. Real risk starts at 20F or colder, the point where pipe material is most likely to crack under pressure, according to Happy Hiller.

At 20F, an insulated line takes about 6 hours to freeze and an unprotected line can freeze in as little as 3 hours. At 0F, an insulated line can freeze in about 4 hours and an unprotected line in 2 to 3 hours, according to Happy Hiller.

Pipes buried well below the local frost line freeze far less often than shallow ones. Frost depth varies widely by region, which is covered later in this article along with who pays for a frozen line.

How to Thaw Your Underground Frozen Pipe

Safe options include a ground thawing blanket, a space heater on an accessible entry point, hot water flushed through with a pump, or an electrical thawing machine on metal pipe. Never use an open flame; it is a fire and steam-burst hazard, according to Powerblanket.

Ground Thawing Blanket

Wrap a heated blanket around an exposed section near the curb or house entry point. This is the safest method and takes 8 to 24 hours, according to Powerblanket. Expect to pay roughly $50 to $150 to rent or buy the equipment.

Space Heater or Heat Lamp

Place it where the line enters your house, kept away from anything flammable. This works in 30 minutes to a few hours, but only if the frozen section is short and reachable.

Hot Water Flushing

A submersible pump pushes hot water through the line from an accessible point. It needs access at both ends and can take 30 minutes or longer, depending on how long the blockage is.

Electrical Thawing (Metal Pipes Only)

A low-voltage, high-amperage machine sends current through copper or galvanized pipe to generate heat, and can thaw a service pipe in as little as 10 to 20 minutes when both ends are accessible, according to a classic plumbing reference, Chest of Books. It does not work on plastic PEX pipe.

Excavation and Direct Heat

When the line sits under a driveway or foundation, a plumber may need to dig it up to apply heat directly. This is a last resort, tried after other methods fail. A damaged water meter sometimes turns up during this process, since thawing pressure can shake loose a weak meter connection.

Never point a propane torch, blowtorch, or kerosene heater at a frozen pipe. Open flame can crack the pipe further or start a fire, according to Powerblanket.

When to Stop Thawing and Call a Professional

Call a plumber if you see no change after 8 hours of continuous heat, if you cannot find the frozen section, or if multiple fixtures have no water at all. Also call if you see any leaking during or after thawing, or if you have plastic PEX pipe.

Professional thawing typically costs $100 to $200, and can run up to $500 for a deep or hard-to-reach line, according to JustAnswer. A plumber also has equipment DIY methods cannot match for buried lines.

• No water after 8 hours of continuous heat application
• You cannot locate the frozen section
• Multiple fixtures all have no water, which may point to the main line
• Any leaking during or after thawing, meaning the line has already burst
• The frozen section is under a driveway, patio, or foundation
• Your line is plastic PEX pipe, since electrical thawing will not work on it

Who Pays: City Utility vs Homeowner Responsibility

Your water utility owns the main and the line up to the curb box; you own the service lateral from the curb box to your house, according to Minneapolis Public Works. Call the utility first when you have no water so they can check their side.

If the city's line is frozen, they thaw it at no cost to you. If your side is frozen, you pay for thawing and any repair, per Minneapolis Public Works.

1. Call your city's water emergency or non-emergency line and give your address and meter number.
2. The dispatcher will ask whether you have any water at all, even a trickle.
3. The utility checks the main and may send someone to your property.
4. If their line is frozen, they thaw it at no charge.
5. If their line is fine, they will tell you the problem is on your side and to call a plumber.

If water is leaking at the curb or in the street instead of just not flowing, the problem may be the water main itself, not a frozen service line.

Cost of Thawing and Repairs

Thawing an accessible line costs $100 to $200 from a plumber, or $50 to $150 if you rent equipment yourself, according to JustAnswer. If the pipe has already burst, excavation and repair costs come on top of that.

Trenching to reach a buried pipe typically runs $5 to $12 per linear foot. Repairing or replacing the damaged section then runs roughly $100 to $200 per linear foot.

If the line has burst, burst pipe repair options and typical costs cover what a plumber will likely recommend next. Homeowners insurance may cover the water damage from a burst pipe, though usually not the pipe itself, and not a failure caused by poor winterization.

When to Excavate Instead of Thawing

Excavate when the frozen section sits under a driveway, patio, or foundation, or when thawing has failed after 8 or more hours. Also excavate if the pipe has multiple sharp bends or shows visible cracks or rust that make rupture likely during thawing.

Digging up a line costs more upfront, but it also lets you bury the new line deeper and better insulated, below the local frost line as your area's plumbing code requires. Codes like the International Plumbing Code set the minimum cover for exterior water pipe.

Frost depth itself varies a lot by region, running much shallower in the South than in the North. Check with your local building department or public works office for the exact frost depth and minimum burial rule where you live.

• The frozen section is under a driveway, patio, or building foundation
• Multiple 90-degree bends in the frozen section block heat transfer
• DIY or professional thawing has run 8 or more hours with no success
• The pipe shows visible rust, cracks, or age that raise burst risk during thawing
• The same line keeps freezing year after year, suggesting it is buried too shallow

Burying a replacement line deeper and insulating it well can stop the same spot from freezing again next winter. See our full guide to preventing frozen pipes this winter for a complete seasonal checklist.