I have permatherm electric radiant cable heat on concrete slab, self leveling, then tile. Worked great for a few yrs then now, keeps tripping off when trying to turn it on. Are there problems that can develop with cables over time? (hope not!) Or would it be a controller/thermostat issue?

With a ohm-meter (or milli-ohm meter) you should be able to tell if there's a dead-short on the element cables, base on their rated power and operating voltage.

Make sure there is no short to the ground lead from either element lead. Then call the manufacturer to find out what the ohm's reading should be for the element you installed. Then check the reading between the elements to be sure it's within 5% +/- of what the reading should be.

I have never had that problem...my bad. hehehee

Nice to hear from you again warms.