I woke up this morning to find a trickle of water pressure to my cold bathroom taps, and no water pressure to my hot water bathroom taps. The water was fine in the rest of the house. Since we're in the middle of an unusual cold snap (20 degrees) in Portland and this bathroom is always the coldest in the house (old, weird insulation), I immediately assumed froze pipes.

So far I shut off the water main because I'd read it's actually the water pressure that will cause a pipe to burst. My plan was to wait it out until tomorrow (the temperature is supposed to climb and stay above freezing)

Is this a sane plan? Is there anything else I could do to fix this short cutting a hold in the drywall and taking steps to preemptively defrost the pipes? Anything else I should know?

Update: Good information below, adding this illustration I found that cuts through some of the confusing language people use w/r/t the bursting problem.

illustration of bursting problem http://www.portlandoregon.gov/shared/cfm/image.cfm?id=338768

  • One winter when I lived in Scotts Valley, CA, (south of San Jose) we had an unusual cold snap and many people's pipes froze. Having no experience with this kind of thing, some people called the police. Your mileage may vary. Dec 9, 2013 at 14:28
  • 3
    Do not call the police. Call a plumber.
    – DA01
    Dec 9, 2013 at 16:03

6 Answers 6


The bursting is actually caused by the ice. Ice takes up more room than the amount of water it was made from, ultimately bursting through copper.

If you had a trickle of water, you may have been better off leaving the taps all open in hopes of keeping the water flowing. Flowing water (even a trickle) is less likely to freeze than standing water. One of the ways to prevent frozen pipes is to leave the taps open to a trickle (obviously not a good long-term solution, but can work in a pinch in locations with rare temp drops). The open taps also allow for lateral expansion of the water that may freeze.

At this point, if the pipes are frozen solid, and are behind walls so that you can't get to them, you pretty much have to wait it out and hope they haven't burst. If they have, depending on how many places they burst, you may be able to go in and fix a few patches. But if there's more than a few splits, you may end up wanting to pull the whole thing out and replacing it all (and this time ensuring everything is properly insulated).

Good luck!

  • Thanks for the advice DA01, it's appreciated — are you sure about the radial expansion of the ice that causes the splits? I've found numerous references online that attribute the splits to pressure between the closed faucets and the growing ice downstream. robertpowersins.com/Newsroom/newsFrozenPipes.html Dec 9, 2013 at 2:05
  • Yes, that's what causes the split. Ice expanding outwards. If it can't expand in either direction, it can only expand out. Shutting off the water may help--especially if the shut off valve is in a conditioned (heated) space in the house so that the pipe doesn't freeze in that section. But once you have two spots frozen and then the middle starts freezing, it can only go out.
    – DA01
    Dec 9, 2013 at 3:18
  • 1
    As for that linked article...it's a bit contradictory. But the article's point, which is valid, is that it's not the initial freezing spot that causes burst pipes, it's subsequent ones that no longer have any room to expand laterally due to the first freezing spot. In the end, it's still an outward expansion of the ice that will split the copper (or PVC) pipes (PEX can survive freezing a bit better). Shutting off the water at the main is still blocking water from expanding, even though you no longer have the water pressure. So I'm not sure that does a lot in and of itself.
    – DA01
    Dec 9, 2013 at 3:20
  • Oh...but here's a thought...if you shut of your main AND you can open up-stream faucets from the frozen one, THAT could help...as that would reduce the water stuck in the system allowing for expansion room.
    – DA01
    Dec 9, 2013 at 3:24
  • 2
    The shut main may help to keep flooding to a minimum in the event of a burst pipe, but it does allow pressure to build up between any frozen spot and the main shuttoff. If the main shutoff were open, the pressure upstream of the frozen spots would never rise above the normal supply pressure.
    – mac
    Dec 9, 2013 at 15:50

I live in Alaska. Relax, your pipes aren't going to burst due to 20 degree weather, even if your house wasn't plumbed with cold weather in mind. You don't need to take any preemptive steps beyond turning the main back on and keeping your tap set to "trickle". That's it, wait it out. It'll be fine. Trust me on this one, I know of frozen pipes.

  • 2
    My guess is that if you live in Alaska, your pipes are properly insulated, though.
    – DA01
    Dec 9, 2013 at 16:05
  • @DA01 Yes, of course they are. If we were talking about sub-zero temps I would not be so casual about it. But 20 degrees? fagedaboudit Dec 9, 2013 at 20:28
  • 1
    Right, I guess my point was that the pipes in Portland may be incredibly poorly insulated (or not at all) which may make 20 degree weather a problem in Portland while it's not so much in Alaska.
    – DA01
    Dec 9, 2013 at 22:23

If you have a trickle, you want to let it trickle. More than "being less likely to freeze", in the situation you describe it will very likely melt through the plug. Ground water is generally 50 degrees or so, and municipal water, while often cooler in winter, is at least something above freezing, so any flow of water will gradually melt out the ice.

For the hot water pipe that has no flow, you can open the faucet and hit any exposed metal pipe where it comes out of the wall (but your pipe may not be metal) with a hair dryer, which will conduct some heat into the wall section of pipe - if you have access below, hit both sides. If not a metal pipe this will help less in general, and more from below if it helps at all.

If you are going with "shut off the water" you need to drain the pipes as much as you can, or you won't reduce the pressure a bit by shutting it off. Open a tap up high and a tap as low as you can (air will go in the upper one.) And, of course, the taps on the affected sink, for the downstream side of the pressure problem.


I am in Portland too. Tonight is expected to be cold again, perhaps even colder. (I observed 6 °F at about 03:00 Sunday morning, elevation 300 ft.) I think turning the water off is not an optimal decision.

It would be better to have water flowing through the pipes, especially where they are exposed to low temperature. City water and most of the distribution system has 45–50 °F water, so if source water flows past partially iced pipe, it will melt it causing the water to flow even more freely.

Turning off the water will allow the pipe cross section to freeze solid and that will burst pipes. If a pipe is already frozen solid, then turning the water off is a wise move: it prevents flooding when it thaws.

If you have a crawl space under the house, are all the foundation vents blocked? For pipes under there, this should be more than enough to prevent freezing. The ground is naturally about 50 °F (the year round average temperature), and by allowing that to moderate the airspace temperature, it will prevent freezing for many weeks. I can't recall there being below freezing temperatures for more than three weeks and that was 1972 or 1973.


First, as others have pointed out, a trickle is good. It means the pipes aren't frozen solid.

Second, the pressure has nothing to do with the pipes splitting. The expansion of water as it freezes causes the pipes to split. Once they're frozen all you can do is cross your fingers as they thaw.

Third, if you have copper pipes you may get by with having them freeze. They can typically freeze more than once before splitting.

Turning off the water was wise since at least one pipe seems to be frozen solid. Sometime around mid-day tomorrow (after it has warmed up) turn the water back on, preferably with someone in the bathroom to listen for water spraying inside the walls so that you can react quicker to turn it back off if that's the case. If you don't hear anything, you're probably in good shape. If the pipe has split it should be audible. At that point you'll need to call a plumber and they will bust through the drywall to repair the pipe.

Given that you live in an area where it doesn't often get very cold, you can simply set your faucets to drip during snaps such as you're experiencing. Be sure to set both hot and cold to run slightly. Flowing water will not freeze as easily, and obviously the water further down the pipes is not as cold.

If you want a more permanent solution (or if the plumber ends up knocking a hole in your wall) take the opportunity to pack some fiberglass insulation between the outside wall and the water pipes. If you do it the other way around it will only worsen the problem. Only insulate against both walls if there is an obvious outside draft running between the walls.

If you're really worried about it happening again you could replace the pipes with PEX but that's going to be more expensive than just packing insulation around the affected area.

  1. Turn the main back on. The trickle was good.
  2. Open all your taps to a trickle.
  3. Run a moderate stream of hot water to the nearest hot tap to the bathroom.
  4. Run a hair dryer on the pipes in the bathroom.

Your hope is the trickle turns into a torrent sooner rather than later. A trickle is enough to prevent freezing, and might be enough to melt the ice plug you've generated, especially if it's a hot water trickle involving actual hot water.

Else turn the main down to a trickle to prevent floods, leave the other taps at trickle, and try again mid-morning as things warm up.

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