I repair a fair amount of ceilng radiant heat here in Indiana. The folks that have it turn down the option of baseboard heat almost to a person. They really love the ceilng heat.
I use a tic tracer, and disconnect one half of the 230v feed to the thermostat, and then by-pass the t-stat. Turn the circuit back on, use the tracer to follow the cable up the wall, then in the tight loops across the ceiling. When you run out of signal, mark the spot (pencil) the repeat the process with the other half of the circuit. If it runs out in the same place, you've found the break. If not, keep at it. A lot of it is learned experience, and figuring out how the ceiling loops are run. They are installed in loops back and forth across the ceiling, usually 4" apart, from one end to another. The wires are usually sandwiched between two layers of drywall, or plastered onto an existing layer of plasterboard then another board is added and plastered again.
A tip is to find and look at the crimped connections between the resistive wire in the ceiling and the wires feeding them from the t-stat. They seem to disintegrate first. Second tip is to look for anything added to the ceiling through the years. I've patched more than a few right at a swag hook installed fairly recently. Third tip, repair guys often repair water damage by removing the first layer of plaster/drywall, then screwing the patch piece to the ceiling without thinking or knowing of the cable heat. The screws often just nick the wire, and the wire lasts some time before finally burning through. Patches could be a few years old before any trouble shows, so ask about older patches as well as very recent ones.
Tell the folks you're doing the work for that it's often time-consuming to repair the heat, but well worth it.
Didn't there used to be a section in the American Electrician's Handbook on installing ceiling heat? If you know how it's installed, it's easier to visualize how to find and repair it.
edited for late night, two fingered typing.
[This message has been edited by Dallas (edited 12-05-2004).]
