Big freeze, new house. Just found out the add-on bathroom was plumbed by amateurs, and the cold water supply froze. I don't have access to the frozen section of pipe (without major demo), so I can't heat the pipe directly.

If I open the hot and cold tap on the sink faucet at the same time, while also opening the cold tap on the tub in an adjacent bathroom (which is also affected by the frozen pipe). The hot water backflows through the diverter of the faucet, and comes out in the tub. I'm using this backflow technique to try and heat the pipe enough to hopefully, break up the ice in the pipe.

All this got me wondering. If I have a plumber come out, is there anything they can do? Do they have a special tool or technique to deal with this situation? Would the plumber simply want to start cutting holes in the walls/ceiling to gain access to the pipe?

More info:

The water supply for the second bathroom seems to be tapped off the tub supply lines of the original bathroom. In the original bathroom the sink and toilet work, but the cold supply for the tub does not. This means that the frozen section of pipe is after the sink in the original bathroom, but before the tub in the same bathroom.

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Rough sketch of cold water plumbing

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Rough sketch of cold water plumbing highlighting suspected frozen section

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Rough sketch of cold water plumbing showing hot water backflow path

  • 8
    I think most plumbers just open up the walls, especially since it isn't their job to close them back up. You'll want to do this eventually to properly fix the issue (adding insulation or moving pipes) so you may as well get started now.
    – BMitch
    Jan 7, 2014 at 15:09
  • 9
    I think the reason the plumber will open the walls to thaw the pipe is because if it's frozen solid enough that no water will flow, then it's likely that the ice has caused the pipe to burst and as it thaws you're going to end up with a big leak (hopefully you'll see the leak immediately and the water doesn't follow some in-wall penetration to end up flooding the basement before it's noticed).
    – Johnny
    Jan 7, 2014 at 20:47
  • If there's any way to blow that warm air into whatever wall space the pipes go through, say a vacuum cleaner on reverse, that can help. You don't need to thaw the whole pipe, just enough of it to get a little flow out through the faucets. The flowing water will do the rest of the job. Feb 21, 2015 at 2:50

7 Answers 7


If it's a metal/copper pipe, you could wrap the exposed portion of the pipe in heat tape to help speed the thaw. Since metal and water are good conductors of heat, the heat from the tape will spread fairly quickly down the pipe.

Or even just use a hair dryer. Not as efficient or quick, but still helpful.

  • we use a hairdryer to deal with the every-few-years freezing of the underground supply line from our well to a basement pressure tank. Takes about 30-60 minutes: faster than a plumber would even arrive. If it wrecks the hairdryer I'll replace it, but it hasn't yet :-) Jan 7, 2014 at 20:09
  • I don't have much access to the plumbing. There is a short nub with shutoff under the sink in the second bathroom, and a nub with shutoff near the toilet in the original bathroom. The rest of the plumbing is inaccessible. Not enough exposed plumbing for heating cable.
    – Tester101
    Jan 7, 2014 at 20:28
  • 1
    Then as @bmitch suggested, cut open the wall in the cabinet. That's a good place to hide your handiwork.
    – longneck
    Jan 7, 2014 at 20:40

If it's a metal pipe, call a weldor. Pipe thawing is a normal use of large portable welding rigs. You put a clamp on either side of the frozen spot and run current through it until it thaws enough for water to flow - the flowing water will remove the rest of the ice. Edit: Hmm - evidently this is less common than it used to be due to idiots and lawyers, but there may be "pipe thawing machines" that are more idiot-proof. I know we used to call the weldor to thaw our well-water pipe before we replaced it with a more deeply buried plastic pipe, 40 years ago. But he wasn't an idiot, so nothing caught on fire and he didn't ruin his welder.

If plastic, you're going to need to supply heat, or wait for it to thaw. If you run the water nearest the issue it will conduct a bit of heat into the pipes. If you can point a heater into a crawlspace it may also help.

What you are doing with the hot water flowing to the tub is a good idea on this line. Edit: it will also help heat the space where the cold water pipe is frozen, assuming the two run together through the walls.

  • 2
    For outdoor use, I can definitely see using a welder to thaw out pipes, it can save a lot of trenching and isn't likely to catch the soil on fire. But I wouldn't want to do it for a pipe inside the walls of my house, if the pipe already burst behind a wall in such a way that it's hanging together by a small remaining piece of pipe, that remaining piece of pipe is going to carry all of the current and get extremely hot -- possibly hot enough to ignite a stud or other flammable material.
    – Johnny
    Jan 7, 2014 at 20:44

You could attempt to raise the temperature in the room high enough to thaw out the pipe. Grab a couple of space heaters and close up the vents and under the doorways.

You could also rent a couple of torpedo heaters from your local tool rental, and try and heat the wall from the outside (I would not do this if you have vinyl siding or another material that will not stand up to direct heating).

Disclaimer: You will of course have to follow the proper safety precautions for using heating equipment in/around the house. Do not leave them unattended, remove all flammable materials nearby, be aware of ventilation concerns, etc.


I placed small heaters in front of the kitchen sink cabinet and in front of the bathroom sink cabinet. I also placed one in the laundry room where my hot water heater and pipes are. After about 20 minutes the hot water began to flow. Hurray!


Upon awaking after 5 hours, I had no running hot or cold water in my kitchen sink. Temps had dipped into single-digits, and I had forgotten to trickle-drip the water here. The adjacent laundry room and bathroom had no problems apparent. I had my sink moved to a different location during a recent kitchen re-modeling; as a result, the contracter ran the hot and cold pipes close to the outer brick wall. With the help of a skilled, patient neighbor, it took time and several tears in the sheetrock wall at various locations, before we figured out where the freeze actually was. After finding this spot, the hairdrier worked within 45 seconds in thawing the pipe: restoring water flow into the sink, related water filtration and dishwasher pipes. I had tried the hairdrier under the sink, however the freeze was actually about 8-10 feet down the pipe, in the adjacent laundry room. I don't believe any reasonable length of time would have thawed this pipe with hairdrier use directly under the sink, since the freeze was quite far down at the other end. Interestingly enough, this laundry room doesn't have sufficient heat running into it, so the pipe tends to get quite cold, especially in these frigid temps. Heat conduction did not seem to help this situation, until I started directly at the freeze source to free up that section sending water flow even again. I shall never forget again to run the water in a simple trickle, in order to keep it moving to not freeze. Thank you all for these valuable techniques, especially the hairdrier tip.


I had a problem with pipes in my bathroom and utility room. The temperatures had been well below zero and windchills to -30 and -40 degrees. Everyone in the area had problems and it was impossible to get a plumber out. Luckily I found some good information online.

The bathtub drain froze but water still came out both the faucets. I had standing water in the tub so I got almost all of it out using a bucket. Then I took about 1/2 cup cooking salt (all I had on hand was sea salt) and poured it right over the drain opening. The salt sank into the drain pipe even though there was still water. I checked 1/2 hour later and the water was still in the tub. I put another 1/2 cup of salt in the drain. I checked 1/2 hour, an hour, and 2 hours later and the water still hadn't gone down. I gave up, thinking it wasn't going to work. I checked it again 3 or 4 hours later and the water was gone! I ran hot water down the drain and it was fine (it gurgled a lot at first). The drain has been open ever since (that was one week ago).

Also that same night I had frozen pipes in my washtubs (opposite end of the house as the bathtub). Water would not run out of the hot or cold faucet. The pipes are in the walls and a plumber would have to tear part of the wall out to deal with it. I shut the water off to the house and opened the washtub faucets part way. Around 9 pm I turned the heat up to 69 degrees in my house. (I had been keeping it at 63 degrees at night and 65 during the day). 2 hours later I heard a drip coming from the washtubs! I kept the water shut off to the house. When I went to bed (about 5 a.m.) I turned the faucets off but I think now I should have kept them open. In the morning I called a plumber and he told me to open the faucets and turn the water back on. The water flowed fine and has ever since.

The plumber said I got frozen pipes because I'd been having my thermostat too low with the weather being so cold. He said if the temperature outside is below zero then the thermostat should be set to 72 degrees.


People think that leaving a faucet trickling will keep water flowing but that's not the reason for keeping the faucet open because if it's cold enough even trickling water will freeze. The reason to keep the faucet open is to release pressure to prevent a burst pipe. Inside a pipe there is air and water. When water freezes it expands forcing the air that's trapped in the pipe to move toward the faucet end. If the faucet is closed there is no where for that air to go. It's this trapped air, which has no place to go, that burst the pipe, not the water in the pipe.

  • 3
    I'm not versed in the physics of burst pipes, but I would expect the expanding ice to be the cause of the pipe damage.
    – Tester101
    Feb 16, 2015 at 13:03
  • 1
    @Tester is absolutely right. Air is easily compressible, water not so much.
    – Doresoom
    Feb 17, 2015 at 20:30

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