I'm looking to buy thermostats for all of my 14 Radiators. These talk to a Kasa Hub (hoping I can link in with my Tapo Smart home too)

But I don't understand how it controls the boiler.

I currently have a Firebird oil boiler - this has a Hive connection wired to it. I then have a thermostat in the Hallwall which i use to control the Hove, of Via an App.

However, if I want to switch to KASA range, I feel like the kit is missing the part that connect to the boiler?