Most newer furnace models are designed for reliability, if maintained well, over a long period. Furnaces are one of the most needed and expensive appliances in almost every household. Reasons for your furnace not working can be complicated or straightforward. You are better off leaving the complicated problems such as wiring, faulty thermocouples, blower motors, and heat exchanger to a qualified HVAC professional. However, there are a few things you may check before contacting an HVAC repairman for furnace repair service, saving yourself money. One of the most likely reasons your furnace is not working could be dirty or clogged air filters. A clogged filter can restrict airflow into your system, causing your system to work harder than it is designed to and ultimately shut down. If the air flow out of your registers or vents seems low, check for clogged filters. Ensure that all your registers are open and not obstructed with objects or dust. Not working furnaces could imply faulty pilot ignition light. If your furnace clicks on or initiates the start cycle but fails to fire up, you probably have a faulty ignitor/sensor. Under normal operations, your furnace is prompted by the thermostat to click on. Your ignitor becomes red hot. It initiates the entire heating process of ignoring your gas and blowing the warm air into your living space. You may also be dealing with a simple reason as the power to the furnace is off, causing your furnace not to work. Their circuit breaker may have tripped or a fuse blown. The power switch has to be in the ON position for the furnace to work.