Originally Posted by Shiela G
Furnace has been acting up for a month. We replaced the programable thermostat the furnace came on this morning and then has not come on since temp is at 70 down to 65 in house has not turned on?
your furnace has been sending you a message for the past month.......that something is not right. Obviously it was not the thermostat, after all you changed it and you still have issues. I have worked on many furnaces just like yours, and although it could be many many different things, the most common problem with your furnace, and thousands just like yours is a dirty flame sensor.
What it has been doing for the last month is going into a soft lock out, resetting itself every 3 hours, now the condition has gotten worse, the control boards See's that and is putting it self into hard lock out. when you turn the furnace off and back on you reset the control board.......and the processes starts all over again.
The flame sensor is a steel rod with a white porcelain base opposite side of the burner rack from the ignitor. the ignitor is the thing that glows bright red or orange when the furnace starts. Remove the flame sensor (usually 1 single small screw holds it in) clean it with steel wool or even the green sponge pad that many people us to do there dishes (the pots and pan side). 99% of the time this will get you back up and running.