Your furnace has several carbon monoxide safety switches that cause the heating to stop working. If the furnace door is off the unit, then this could be a reason the heating wont run. A bad fan or rusted inducer draft motor will let the furnace circuit board know that carbon monoxide will not be removed from the heat system. Your furnace shuts off if you have a faulty heat exchanger has a hole in it because the furnace gets too hot. A high temperature switch cuts your furnace off so carbon monoxide doesn’t leak outside the heating system. The shut off switches on furnaces have been used for years and Air Heat Raleigh is experienced with the many different types of heating repairs you need.