How to splice repair an electric floor heating cable using butt connectors 

It is very important to solder all splices and then apply a heat shrink with internal sealer.

since the two current carrying wires look identical, how can I tell them apart when I splice them back together?

Hi, Good night, I have electric underfloor heating on the floor. and broke down last winter. I opened a hole and managed to find a cut wire. My thread is exactly like yours. I have a doubt, these two wires have to have continuity with a multimeter between them despite being a resistance

Hmmmm does it matter what wires you splice together?