My furnace will periodically only turn on when you manually drop the set temp on the t-stat below the actually temp and then bring the set temp back up or if I cycle the unit off/on at the furnace. The furnace is 5 years old, Lennox Signature G60UHV-60C-090 and had a Comfort Sense 7000 up until a week ago when I changed it out for a new Honeywell. This change was unrelated to this problem...programmable model that you can control on-line that my wife wanted...although it did confirm that it was not a t-stat issue as problem has been happening with both. With new t-stat, I can even see that it goes from "Heat Mode" to "Heat On" when the call for heat is made. I tried to search other posts where people have had the same problem but with no luck. My guess is that it is may be a simple fix that I can do myself. Just not sure what. Any help is appreciated before calling the big guys in.