Exposed Frozen Pipe
If the frozen pipe is exposed, then you have several options available but first here are some notes to remember. When working on thawing the pipe leave the main water valve open (near your water meter) and remember to heat the pipe from the faucet toward the frozen area. This way, the water can flow out as the ice melts and the water pressure in the pipe will force the ice out once it melts sufficiently.
Techniques for Thawing an Exposed Frozen Pipe
One of the best and safest ways to thaw the pipe is to heat the area with a high power hair dryer. Again, make sure to open the faucet and then heat the pipe working back from the faucet toward the frozen blockage.
Also, if the pipe is close to the wall, place a cookie sheet behind the pipe to help radiate heat onto the back side of the pipe.
A heat lamp works well to heat an exposed pipe. You can use an infrared or incandescent heat lamp. As before, if the pipe is close to the wall, use a cookie sheet behind the pipe to help reflect heat onto the pipe.
Infrared Heating Lamps
Small Portable Heater
If you have one of those small powerful heaters they work great when warming pipes under a kitchen or vanity base cabinet. Direct the heater onto the frozen section of pipe. It will work like a hair dryer on steroids!
Electric Pipe Heat Tape
Another technique is to use electric heat tape. This is a ribbon type wrap that has electrical heating elements in it. You wrap it around the pipe you want to heat, and plug it into the wall. The temperature is controlled with a thermostat and the heat tape heats the pipe.