I had 5 wires to work with from the boiler room to the thermostat box, the original clever thermostat only needed two. Sending power to the micro-controller without adding dissipated power that could disturb the thermometer was a bit challenging. 

In the video, a last flight check before putting everything back together. You can see how the set point moves all the way  to minimum and then advances to the set point. Check the project details (or the Github code!) if you wanna know what's going on.