In the Nick of Time
Sometimes pipes freeze but don't break. This also causes problems, as the frozen water blocks water to faucets and appliances. If this happens, thaw the blockage before it breaks the pipe and creates further damage. To do so, you'll have to locate the blockage. Leave the blocked faucets or valves turned on to equalize pressure as much as possible, then trace the pipes back from there, feeling along the pipes for the coldest spot. Pay particular attention to exterior walls and unheated areas, which are common locations for pipe breaks.
Freezing weather is the leading cause of pipe breaks. As temperatures plummet, water expands. As it does, it causes localized pressure that normal metal pipes can't handle. This can cause one of the following:
A pinhole leak
A hairline break
A big crack
Thawing is the immediate fix for frozen pipes. Find the coldest part of the pipe with your hands. That's where the block is, and where you want to apply heat. Use any of the following, but don't heat the pipes too quickly. Doing so might make the water in the pipe boil, which can burst it. If you're warming plastic pipe, be extra careful, as too much heat can cause even bigger problems, and follow the specific recommendations below:
Heat gun. Set the gun on low, and keep the nozzle moving near the frozen section but not right on it. If there are flammable materials near careful about overheating them. Heat guns typically come with shields. If yours did, use it. You can use a heat gun on plastic pipe, but keep the gun distance away from the pipe.
Hair dryer. This will take longer, as hair dryers can't reach temperatures that heat guns do, but it's a good approach (and a safer one in general) if you don't own the former. Again, be sure to keep the nozzle of the dryer moving to minimize heat buildup, and be careful around flammable materials. This is a better method than heat guns for plastic pipes.
Electric space heater. Same cautions as above.
Heat lamp. Same cautions as above.
Electric blanket. Probably one of the safest methods, although it can take awhile. Simply wrap the blanket around the pipe and turn it on.
Electric heat tape. Also known as heat cable, this is plastic-coated wire that's wrapped around a surface to keep it from freezing. Be careful with this stuff; the U.S. Consumer Product Safety Commission has issued a safety advisory on electric heat tape, as it can cause fires if not installed correctly or if it's allowed to deteriorate. There are different kinds of heat tape, so be sure to buy the right kind for the type of water pipe you need to treat and read the instructions before installing.
Light bulb. Take the shade off a lamp and place it near the pipe.
You can also thaw frozen pipes by wrapping them in rags or towels and pouring hot water over them. Whichever method you use, keep doing it until the water flows. As the ice thaws, you should see water start to drip out of the faucet. If there's a breakin the pipe, you should also see drips of water where the break is.