Instructions for the floor I laid some 15 years ago said to use a pocket, i.e. a pipe which the probe fits into, with the idea it can be renewed, however it was found when I tried to renew the probe was stuck and could not be removed, the floor was in a wet room so nothing on the floor, so I tried running without the probe, I found that even on 24/7 the floor only reached 30°C and the limit is 27°C so I took a chance and ran it without a probe.
Today reychem underfloor heating does not need probes, the heating element is made so as it warms up the resistance increases, so is self regulating, only the cheap underfloor heating needs a probe, the problem with a probe is it only works where it is fitted, and the heating mat covers a very large area so it is of limited use anyway. It only really works with wet room or similar where there is never anything on the floor, when I fitted it in mothers wet room the reychem version was not enclosed in an earth braid so could not be used without laying an earth mat above it, so could not use it.
We found it was useless really anyway, once the floor had been dug out to put the insulation down and move drains, the floor was so well insulated even with the under floor heating off it never got cold, idea was to dry the floor, with heating on floor was dry after 2 hours if not mopped, and without it was dry in 2.5 hours, wanting a wet room at 22°C with a max floor temp of 27°C and a hall at 18°C with a bathroom extractor running it failed, had to have towel rail on to get room warm enough and switch fan on when leaving room not while having a shower.
The thermostat was just outside the wet room, so it really did need in theory some remote sensor, but found the heating was so useless anyway in practice worked OK without one.