If it's just a relay then wiring it into the actuator then that'll switch it on and off. They can place the electric switch LW934 in the place they want the temperature referenced or use a thermostat
This would depend on the type of underfloor heating control which is used. If it uses an electrical current to switch a motorised valve on and off, then it will be best to use our Electric Switch JSJSLW934. This can be wired to the motorised valve, and use itself as a temperature reference, or a Home Thermostat if desired.
If it is a Wet Underfloor system using hot water running through it you will need a TRV and if it is an electric system you will need a Electric Radiator Switch.