If it’s anything like my setup (posted in the thread) they’ll have a colder spot in the house, whereas the thermostat is in a warm part of the house.
My Nest heats to 22 degrees C but the whole house temp is a couple degrees lower than that.
When the whole house temp hits 20 the heating is switched off, but looking at the thermostat you’d think we’re heating the house to a silly temp, when in fact there’s a disparity between the thermostat temp and the temp of the whole house.