Great post this sort of information is massively helpful to beginners and even experts as it clearly outlines the correct method. You would not believe the stories we could tell of what some people try and do when laying ufh.
The only information I would add is how to test the mat prior to laying it.
1[SUP]st[/SUP] Never connect the mat or cable to the mains power when rolled up as the heat in the middle of the role has nowhere to go and the cable will simply over heat very quickly.
You mention testing it during instillation and the watchdog that the mat you fitted came with but what if this is not supplied. Having a cheap multi meter £5-10 ish we have found is the best way to test mats. You can do a simple continuity test, resistance reading and insulation test all of which can be very useful readings and very easily obtained with this devise. The better units also have a watchdog type facility which will sound should you damage the mat during instillation / tiling. The reading you can get from these devises can be very useful especially if you ever have problems later down the road.
I hope this adds something useful.
[FONT=&]Andrew Knight.[/FONT]