Replaced old thermostat with rth2300b. Everything works OK except no heat. Fan comes on but the air isn't warm. 4 wires come out of the wall to the control unit:
Red wire missing a label
White wire labeled O
Green wire labeled G
Yellow wire labeled Y

Terminals on unit are labeled:
B, O, G, Y, W
R and RC are jumpered together

Anybody know what I need to change to get the heat on?
I've tried the red wire on R/RC and W.
Thanks,
Micah

Red to R. White to W. Green to G. Yellow to Y. Leave the jumper between R and RC in place. Give that a try and let me know how things work out. If this fails to work, you will need to look in the furnace and let me know what wires hook to what terminals there.