@Ian0 In my case, a gas combi boiler, will start every x minutes (default 3, I set to 10) and will heat the heat agent (water) to the desired temperature (50c, for ex) while monitoring flow pipe temperature and return pipe temperature. If the return temperature difference is less than a threshold (10c, for example) the boiler stops considering that no radiator is using heat or cannot transfer any more heat to the rooms.

So when all rooms are "good" the boiler starts but quickly (10 sec) stops. After 10 minutes it does it again. 

However, if a radiator starts to have its TRV (Thermostatic Radiator Valve) opening, the return temperature (of the agent, to the boiler) will drop noticeably and the boiler will continue to burn gas / provide heat continuosly until the desired temperature is achieved.

So when my KE100 decides to open, the next boiler run will pick it up and provide sufficient heat. This can mean a delay between 1 second and 10 minutes, in my case.

Does my explanation make sense?

  @Ian0 I would recommend you to pair the smart TRV with a smart boiler thermostat, it work great.

But definitely che company should make a starter kit included the thermostat to control the TRVs

I have the Meross combi boiler thermostat to control the on/off of the heating system and the TRV to monitor the temperatures of the various rooms, and the heating system gets automatically triggered by the TRV.