honeywell t6360c wiring

Hang on, I'll just get my crystal ball warmed up.

 

A photo of heat mat or wiring diagram might be useful. Perhaps the make and model of heat mat too.

 

Unless Raychem or the like, the thermostat will have a place for the probe so the mat does not overheat. So you should have line in/out, neutral, earth, and two for probes, so at least 6 on the thermostat when three on the mat. Also likely neutral and earth are designed for multiply wires.

The Honeywell T6360C seems to be a standard thermostat not one designed for under floor heating. Nearly all UFH thermostats are electronic in some way.