The first thing you should do if you believe you have a frozen water pipe is turn off the water to your house, or at least the localized area nearest the frozen pipe. A cracked pipe will not be leaking if it is frozen solid, but as you melt the ice, water may come gushing out. If it is not practical to wait for the pipe to thaw, we recommend that you call your plumber for help and advice. If you decide to thaw the pipe with heat, be very careful.
If the pipe bursts as the water thaws, electrical appliances could get wet and cause danger of electrocution. If you use heat, thaw very slowly using a light bulb, a hair dryer on a low heat setting, the exhaust from a vacuum cleaner, or heat tape. Use your hands to find the coldest point on the pipe where the ice is. Keep the heat moving in that general area, but never apply heat to the same spot continuously.
Even if the pipe is not already cracked, too much heat may cause it to burst. Please keep the following safety precautions in mind. The first, and most important, is never heat with an open flame. The danger of fire and bursting pipes is too great.
The second precaution is to use only heavy-duty extension cords with a ground plug. The extension cord should never be lighter duty than the appliance cord, and the extension cord connections should be thoroughly protected from moisture and exposure to weather. The same is true of the appliance you are using as a heat source.
And finally, light bulbs should be of the trouble light type that mechanics use, where the bulb is protected by a cage, and the bulbs should not be placed near flammable materials.