Prevention is the best cure for freezing pipes. Air leaks through an outside wall suck heat away from pipes and cause the water in them to freeze. Sealing the leaks with expanding foam will go a long way towards preventing freeze ups. When pipes are already frozen, your best bet is to use a thawing tool. An Ice Breaker from Systematics starts at around $800, but if you get lots of calls in the winter to take care of frozen pipes, these tools are invaluable.
