I have a Clayton 1600 furnace that the fans seem to run non-stop. Its not till the fire is almost out before they kick off. It came with a thermodisc, i replaced it with a Honeywell limit switch 80145. So i just put the thermodisc back in the other day hoping that would fix it, it did for the first couple of hours, then the fans would run non stop till the fire was almost out. The furnace has twin fans, and i run them both. I have pretty much the same furnace in my house except that has the big single fan, and that one has a honeywell limit switch. But the one in the house works perfectly. Any tips or advice would be greatly appreciated. Thanks....