What is the purpose of the Controller?

I am wondering what the controllers function is in hydronic floor heating?

I have installed pex in the joist space's for the main floor.
There is 5 separate loops for the main floor, 3 more to be added for the basement once I get it finished.
Hence the 8 loop manifold with a 4 wire actuator for each loop.
I am toying with the idea of putting a thermostat in each room to have individual control. My idea is to have power running to each thermostat on a open contact. When the contact closes it would call on the actuator to open the loop. When the actuator opens the loop it will close a contact calling for the pump to start etc.
I am running a Navian CR-210A tankless hot water supply with a Navain heating box HDC-100. The heating box takes the place of the boiler and use's the hot water from the CR-210A.
The heating box is closed loop type.

The controller would gang all of those actuators and thermostats together, and turn the pump on whenever any one or more zone called for heat. You need the controller to actually run the zone valves properly. Usually, the zone valve manufacturer will have various sized controller boards and smaller ones can be ganged together to handle more valves. Some controllers can control more than one valve per thermostat, so you dont' need a thermostat for each valve.

I still don't get the purpose of the controller.
Won't the thermostat control the actuator?

Do you have a make of a controller?
I could go and see just how it works.

Thanks

It depends on the system you choose. When the thermostat calls for heat, it may have to control multiple things: the zone valve, the pump, and the boiler. Then, since you only have one boiler, and may have only one pump, how do you keep from burning things up when you try to turn things on from multiple places. the controller takes care of that for you.

Alright I got it.
Thanks