Although we own a cable break locating instrument, this is one electrical service that we no longer perform.  We have a different suggestion............

 ............Back in the late ‘60s and ‘70s, when electricity was cheap and we seemed to have an endless supply of it here in the Northwest, thousands and thousands of new homes were outfitted with ceiling cable heat.  The main reason for this was that the initial cost was low but the systems proved to be anything but energy efficient and the comfort level was generally poor.  If you have a room with cable heat that has quit working, and a simple thermostat replacement does not fix the problem, chances are that the cable is broken.  It can be a very time consuming process to locate and repair a cable break and we have learned over the years of performing this service that the same cable often breaks again … usually at a different location. The cause of the cable break is more likely to be a problem with some slight movement of the ceiling board that the cable is imbedded in rather than a problem with the cable itself.  Rather than spend your money on a break repair, we suggest that you take this “opportunity” to install a fan-forced wall heater and abandon that antiquated ceiling heat system. You may be so glad you did that you end up replacing it even in the rooms where it’s still working.

Although our electricians are more than capable of installing any brand of electric heater, we recommend Cadet brand electric heaters to our customers. http://www.cadetco.com/