Hi Folks,

I have a Trane downflow horizonal gas furnace that was installed new in the spring of 2000. It has worked great until now. When the heat is turned on the furnace works fine and supplies heat. When the thermostat is satisifed it turns off. When heat is required again the thermostat clicks, after a few minutes the fan runs but no heat is generated. The fan will continue to run until the thermostat is turned off. If you wait about 30 minutes you can turn the thermostat back on and the cycle repeats. The vent fan runs the entire time the furnace attempts to heat. First, the filters have been changed along with a new thermostat.

Thanks for your assistance,

Coy

Your flame sensor could be dirty clean with brillo pad

If the pressure switch is not closing your system will act that way. When you turn it off and back on you are resetting the control board. Check for a restricted vent, pressure switch tube or just a sticking pressure switch.