I am in the process of installing a new thermostat, but I ran into the problem: new thermostat has 4 ports W, Y, R and G. But the old thermostat has 5 wires: W, Y, G and B. I am not sure where B wire (black color) should go. Do I need to look for another thermostat that has a port for B wire?
The black wire should be for ground. You and try to connect it without the black first to see if everything works ok, if it does tape off the black and tape it to the other wires. If not look at your UPM diagram and see which port is for ground and it should hook up with that wire. But I would double check with the heat pump wiring diagram to see what that black goes to and verify that wire with a multimeter.
