I think this posting would be better in the discussions section of the bathrooms forum but our architect mentioned repairing underfloor electric heating from the ceiling below as a possibility.

My carpenter said a factory guy has a break detector type thing he can find the break with. Yes, you still have to take up that tile and repair the break. I'm 99% sure the one I'm getting is suntouch.

Here is a link that might be useful: warm floor

I've had a change in plans. I am now leaning toward vinyl after stepping on the sample tiles the other morning. My existing vinyl is MUCH warmer. I could put in some fancy vinyl for less money than the heated tile.

we are having a nightmare w/o newly installed (expensive $3000 not from Home Depot) electric heated bathroom flooring! the ceramic tile installer said he oms tested it before mortaring, after and again after the tile was laid. Heat DIDN'T WORK! cost $1500 to rent the machine to find the breaks/the electrictions time. found 2 breaks. repaired. still not working! the machine doesn't pin point the exact location, just general area. now they will be tearing up our whole floor! Tile guy won't stand behind his work and said he won't redo it or pay for the new heat mats we must re-purchase. said he can't afford it. make sure your installer uses the machine that is hooked up to the mat and buzzes if you cut the line rather than relying on just oms testing since it may heat up once then any slight breaks in the lines will fry and come apart. Such an easy job but done by gorillas! we thought no one could have messed up this job but they did! the heat mat rep was awesome trying to help.