If your furnace fails, there are a few simple things that you can check before you call a professional technician.
-Check the furnace filter. A clogged filter can diminish air flow, and can cause too much heat, tripping the limit/safety switches. Replace the air filter and reset the furnace.
-Check the thermostat. A blank screen could indicate a tripped breaker, loose wires, or dead batteries. Check to see if the breaker for the furnace has tripped. See if the thermostat wires are tight at all the terminals. Some thermostats use batteries, so confirm that there are fresh batteries in the thermostat.
-Check the fuses. A blown fuse could cause a furnace to malfunction.
-Check the doors of the furnace. If not installed properly, the door safety switch will cause the furnace to shut off.
If none of these repairs work, call a reputable repair company. A furnace is generally repairable. If a major component fails, such as a heat exchanger or control board, you may want to consider putting your money toward a new, high efficiency furnace, especially if your furnace is more than 15 years old.