The hints of HSPalm are definitely good! Note that if you prefer a more fine-grinned temperature regulation you might consider using a PID-regulated thermostat. A thread about that is here: Thermostat with PID controller.
I do not know about the recommended zigbee relay board. But maybe you have to try to find:
- 24VAC valves; as you are working with a water-filled system that can have leakages, you might want to ommit using mains-voltage here.
- Using a relay board with solid state relays; mechanical relays are prone to wear and tear, contact erosion, and mechanical failures.
For our own house, we developed the ControlBox, but I think that’s a little overdone for only 4 groups. We are using 1-wire thermal sensors (ds18b20), that will prevent you from the battery-exchange circus.