Smart Thermostat set to 20, temp always over 23

I am testing out Tado, so setup only 1 smart Thermostat in an 18sqm room.
The room is set to 20 degrees, but the temp since yesterday is above 23 in the room.
Why isnt it going down to 20?

Note:
Underfloor heating, water based, each room on a different circuit/Thermostat.