SunTouch underfloor heater without floor sensor?
Because the radiant floor could get too hot while the external temperature sensor still indicates below required T.
This could damage the element or part of the floor.
The underfloor heating (water) I fitted had two temperature sensors - one for the ambient and one at the output of the mixing valve to shut down the pump if the output was above a certain value so the pipes did not get damaged through overheating.