Hi, I bought a Drayton wiser kit (one, heating only) to try and keep the temperature in our toddlers bedroom more constant. However... My current thermostat is a digistat 3. It has two wires going into it. One is a constant live. I guess the other completes the circuit when the relay in the digistat flips turning the heat on. The digistat has two batteries powering it. my question... Can I swap my digistat 3 for the wiser hub? My feeling is not because I have no "com" wire? I.e. I can't power it. I cant really follow the wiring diagram though and I don't understand the instructions where it says it is voltage free???? thanks for any help!