Open kitchen and bathroom sink cabinets to allow warm air from the house to warm the pipes. Once you've found the frozen pipe, open the affected faucet all the way, and open other hot water faucets in the house. When the water is flowing in the affected pipe, close all the faucets to a trickle. Do not close the affected faucet until the pipe is completely thawed and the water flowing freely. A propane torch or other open flame will heat the pipe too quickly and may cause it to explode.
Some people recommend pouring boiling water over rags wrapped around a frozen pipe.
The obvious drawback is that this method is messy. Never pour boiling water directly onto a frozen pipe. When thawing pipes with a heat lamp or hair dryer always work from an open faucet toward the frozen area. This will keep steam from being trapped by ice and bursting the pipe. With the faucet open, you can see when the ice has melted.