Hi, welcome to the forum.
What kind of heating system do you have?
The insulation in new buildings is much better these days so this can be a reason for the temperature not dropping.
Another one is that your thermostat is doing what it’s supposed to do: heat when the temperature drops.
Do you have radiators, underfloor heating or anything else and what is used to create heat?
With radiators, it’s easy if you touch them to know what is happening.
If you have a boiler, you can see if it’s running (or not).
I wonder what (if) there is any effect from the -327° outside temperature…
One thing is to integrate thermostats but you also have to control them through an automation - created yourself or a blueprint like this one for instance: 🔥 Advanced Heating Control