How to Handle a Frozen Pipe Before the Plumber Arrives

Why this matters

A frozen pipe is a pipe with a plug of ice in it, and the ice itself is rarely what does the damage. Water expands as it freezes, and the pressure builds in the stretch of pipe between the ice and the closed faucet beyond it. That is where pipes split, often somewhere you cannot see. The split does not leak while it is frozen. It leaks when it thaws, sometimes several gallons a minute, into a wall or ceiling. So the job before the plumber gets there is not just "get the water running again." It is to thaw it slowly, with the main water valve within reach, watching for the leak that a thaw can reveal.

Before anything else: if you can see a split, a bulge or water dripping from a pipe, or water is appearing on a ceiling or wall, close the main water valve now. If water is running near outlets, light fixtures or the electrical panel, stay out of that area and call an electrician or your electric utility to cut the power before anyone goes near it. Leave that power off until the electrician has checked the wet area and says it is safe to restore.

Step 1: Find where the water stops

Turn on the faucets one at a time, hot and cold separately, and note which ones work.

• One faucet has no water or a thin trickle, the others are fine. The freeze is in the pipe feeding that fixture, usually where it runs through an outside wall, a cabinet on an outside wall, a crawlspace or a garage.
• The cold side is out but the hot side works at the same sink. The freeze is on the cold line only, which narrows the search to where that line runs.
• No water anywhere in the house. The freeze may be on the main line where it enters the house, or the water service itself may be frozen underground. That one is almost always a plumber's or the utility's job, and if your neighbors have no water either, call the water utility first.

Then look along the likely route: under the sink, in the cabinet, in the basement or crawlspace below that fixture, wherever pipes run near a cold outside wall or an unheated space. A frozen section often feels much colder than the pipe on either side and may have frost on it.

Why this matters: you cannot thaw a pipe you have not found, and heating the wrong section wastes the time the pressure is building.

Step 2: Know where the main valve is, and that you can reach it

Before you warm anything, go to the main water shutoff and make sure you can get to it and that it turns. On most houses it is where the water line comes into the house: in the basement on the front wall, in a utility room, near the water heater, or in a garage. Clear boxes out of the way. If it is a lever handle, it is open when the handle lines up with the pipe and closed when it is crossways. If it is a round wheel handle, it closes clockwise.

Do not close it yet unless you see a leak. Just know that you can close it in seconds. If the valve will not turn by hand, do not force it with a wrench; an old valve that snaps open is worse than one that sticks. Tell the plumber when you call.

See related: Your Home's Shutoffs: Water, Gas and Electric, and How to Close Your Main Water Valve and Fixture Stops.

What breaks if you skip it: the thaw reveals a split and you spend five minutes hunting for a valve while water runs into the ceiling below.

Step 3: Check the pipe for damage before you warm it

Look closely at the frozen section and the pipe on each side of it. A split copper pipe often shows a long, narrow crack or a bulge. Plastic pipe may show a whitened or swollen spot. A fitting may look pushed apart.

If you see any of that, close the main valve now, before warming, and tell the plumber exactly what you saw. Thawing a pipe you know is split only lets the water out.

Step 4: Open the faucet the pipe feeds

Open the faucet that is not working, on both hot and cold if it is a single mixing handle. Leave it open the whole time.

Why: as the ice starts to melt, the open faucet gives the water and the pressure somewhere to go, and a trickle starting is your first sign the plug is clearing. It also relieves the pressure between the ice and the faucet, which is the stretch most likely to split.

Step 5: Warm the pipe gently, starting nearest the faucet

Work from the faucet end back toward the frozen section, so that melted water can flow out through the open faucet rather than being trapped behind more ice.

Safe ways to warm it:

• A hair dryer on a medium setting, moved slowly back and forth along the pipe, a few inches away. Plug it into a GFCI-protected outlet if one is near (the kind with test and reset buttons), keep the cord out of any water, and do not use it at all if you are standing on a wet floor.
• Warm towels, soaked in hot tap water from a working faucet, wrung out and wrapped around the pipe, replaced as they cool.
• An electric heating pad wrapped around the pipe.
• Raising the heat in the room, and opening cabinet doors under a sink on an outside wall, so the house's warm air reaches the pipe.
• A portable electric space heater aimed at the area, kept at least 3 ft from anything that can burn, on a dry floor, never left running unattended and never in a crawlspace or other tight space where you cannot watch it.

Never use:

• An open flame of any kind: a propane or butane torch, a candle, a lighter, a kerosene or propane heater. Torches start house fires inside walls and can overheat a pipe or melt a plastic one. A fuel-burning heater indoors also makes carbon monoxide.
• A heat gun held in one spot. It can scorch wood and melt plastic pipe within seconds.
• Anything boiling poured onto the pipe. Sudden heat on frozen pipe is how a stressed spot gives way.

Expect it to take a while: often 15 to 45 minutes for a short section within easy reach. Slow is safer.

Step 6: Watch for a leak as the water comes back

When water starts flowing at the faucet, keep the faucet open and keep warming until the flow is back to full strength. Then, for the next hour, look and listen along the whole length you thawed, and in the rooms below it: under the sink, the cabinet floor, the ceiling under the bathroom, the basement below the kitchen.

If water appears anywhere it should not be, close the main valve immediately. Then turn on a faucet on the lowest floor to drain the pressure out of the pipes, and call the plumber back with what you found. Leave the main closed until the plumber has found and repaired the split. When it is reopened, open it slowly, then watch the repair and the rooms below it for the next hour to confirm they stay dry.

Step 7: If you cannot reach it, stop and wait for the plumber

If the frozen section is inside a finished wall or ceiling, under a floor you cannot get to, or in a crawlspace you would have to crawl into, do not cut into drywall or crawl into a tight space with a heater. Raise the house heat, open cabinet doors, leave the affected faucet open, keep the main valve clear, and wait. Plumbers have tools that thaw pipes safely from a distance.

A worked thaw, from first faucet to the hour after

The house: the kitchen sink sits on an outside north wall. Overnight it got down to 8 F outside. The kitchen faucet is a single-handle mixer.

7:05 a.m. The kitchen faucet gives nothing on the cold side and a thin trickle on the hot side. Every other faucet in the house works. That puts the freeze on the kitchen cold line, and the cabinet under the sink is the first place to look.

7:08. Under the sink, the cold supply pipe running up from the floor next to the outside wall is noticeably colder to the touch than the hot pipe and has a little frost on it. No crack or bulge is visible on the exposed part.

7:10. The main valve is in the basement on the front wall, behind a stack of boxes. The boxes come out of the way. It is a lever handle, in line with the pipe, so it is open. It is not closed.

7:12. Cabinet doors open. The faucet handle is opened fully in the middle position, so hot and cold are both open, and left there. A hair dryer, plugged into the countertop GFCI outlet above the sink, goes on medium, moved slowly up and down the cold pipe starting at the shutoff valve just under the faucet and working down toward the floor where the frost is. The floor of the cabinet is dry.

7:40. About 28 minutes in, the faucet sputters, then runs a thin cold stream. By 7:47 it is running at full flow. The hair dryer goes off but the cabinet doors stay open.

7:47 to 8:47. Checks about every 15 minutes: the cabinet floor, the wall under the sink, and the basement ceiling directly below the kitchen. At 8:15 there is a small wet spot on the basement ceiling below the sink, and a drop forming.

8:16. Main valve closed. A basement laundry tub faucet is opened to let the pressure drain out of the house lines. A towel goes in the cabinet, a bucket under the drip in the basement. A photo of the wet spot and the drip.

8:20. Call to the plumber: "Kitchen cold line froze last night on the outside wall. We thawed it with a hair dryer under the sink; the visible pipe in the cabinet looked fine. About half an hour after it was back to full flow we got a drip from the basement ceiling under the sink. Main is closed now." The plumber books the visit and says the likely split is in the stretch of pipe passing through the floor, which is the part nobody could see or reach.

Why the watch mattered: the exposed pipe in the cabinet was undamaged, and if the family had called it fixed at 7:47 and gone to work, the hidden split would have run into the basement ceiling all day at full house pressure.

What would have changed the plan: if the frost had been on a pipe already showing a crack at 7:08, the main valve would have closed before any warming started. If the frozen stretch had been entirely inside the wall with nothing exposed in the cabinet, the hair dryer would have done almost nothing useful; raising the house heat, leaving the cabinet open and calling would have been the whole job.

How you know it went right

• Full flow at the faucet that had stopped, hot and cold.
• An hour of checks along the thawed run and the rooms below it, with nothing wet.
• No scorched wood, no softened or discolored plastic pipe where you applied heat.
• The main valve back fully open if you closed it and the plumber has repaired the leak.

Then fix the reason it froze. Leaving the faucet dripping on the coldest nights, keeping cabinet doors open on an outside wall, and keeping the house heat steady overnight all help; the plumber can tell you whether that pipe needs insulation or rerouting. See related: Frozen Pipe Prevention + Thaw Reference, and How to Get Your Outdoor Faucets Ready for Winter.

References

• See related: Frozen Pipe Prevention + Thaw Reference
• See related: Your Home's Shutoffs: Water, Gas and Electric
• See related: How to Close Your Main Water Valve and Fixture Stops
• See related: How to Handle the First Ten Minutes of a Water Leak
• See related: When to Stop and Call a Licensed Pro Around the House