the fan sometimes will and wont turn on... and the same thing with the heat. now i cant get it turn the heat on at all.
replace it,,they are not safe and i haven't seen one in years,,at least get a co detector
the fan is activated by a fan/limit switch on those furnaces, that just means that the furnace isn't firing and getting the heat exchanger hot enough for the fan to run. I have no way of knowing whats wrong with it without being there, from my past experience the most common repair I run into is the ignition board, other things could be a plugged air flapper - thats the air filter for the incoming air, or plugged condensate line, typically if the furnace will fire there will be water heard slushing in the inch and a quarter vent discharging the side of the furnace at the tee. And actually the most common thing I run into on the furnaces is a bad heat exchanger ecspecially the ones that were made in the 80's. The serial number will tell the age, the first 4 numbers in the serial are the date. ex - 5687, = may 6th 1987. If you have pulse made in the 80's the heat exchanger is getting to the end of its life. Roughly about half of the ones I test don't pass. If you have a 90's pulse you're a little better off. If the heat-exchanger is bad and you are the original buyer Lennox will replace your furnace for you, for the cost the labor would have been to replace the heat exchanger / (the heat-exchanger they no longer make) I recommend calling a lennox dealer to come service your furnace and do a pressure test on the heat-exchanger. If the heat-exchanger is bad there is a threat for carbon monoxide to be present in the house so be ware if the tech finds its bad he'll will lock out the furnace.
