I want to buy a new smart thermostat, but am confused on the old wiring. I have single zone 120year old gas boiler (converted from coal, then oil, now gas). No cooling. The old honeywell thermostat is wired R, W, B, TR, TR with red, white and blue (blueish)wires from the boiler. But also two TR wires, one green and one black. I'm assuming one of the TR wires runs the clock on the thermostat? I'm confused on where each wire would hook into on a new smart thermostat and which is common?