I just purchased a new Honeywell RTH6400 thermostat and after installation when the heater is on, the system does not turn off. Wires from the wall are Y, W, R, B. I installed Y to Y, W to W, R to R and did not install B, as per the instructions. Everything works but the system does not turn off. When Thermostat is in off position, heat turn off and the fan starts blowing cool air. I have a standard carrier central heat and cooling system around 20 years old. I know its a wiring issue.