I replaced my old thermostat with the RTH230B and it seems as though the fan comes on but there is no hot air coming out with the heater setting. I put the wires in the spots that they were in the old thermostat, but there was an extra blue wire that was not connected in the old so I did not connect with the new. The wires that are there, that were hooked up to the old one are; red, yellow, white, and green.