I replaced my old thermostat (mercury type) with the RTH230B. I did not have any problems with the cooling system this summer and seems to be working. Then a couple of days ago I switched to heating. I noticed that when desired temperature is attained, the furnace will turn off (which is normal) then after a few seconds, the fan will turn on again (furnace off) then will turn off after a minute.

Did I do the wiring correctly? I connected the black wire to Rh, red to Rc, white to W, Y to yellow and green to G.

Can someone please help me sovle the problem>

Thank you.

Sounds to me like your fan/blower controller needs to be adjusted. You are having a ghost blower problem. The control is out of adjustment and it is allowing the furnace blower to come back on to remove a small amount of residual heat.

You might check with the thermostat manufacturer. Some have a built in program to turn the blower on after a few minutes to reclaim that heat. If it is the thermostat you can usually program that feature out of it. Read your instruction that came with your thermostat.