Check the thermostat to determine if it is set to “heat.” Many thermostats regulate the heat and air conditioning and, if the thermostat is set on air conditioning, it will not properly regulate heat. At the same time, inspect the power switch for the furnace to ensure it's on.
Inspect the circuit panel for the furnace. Often the furnace connects to the main panel or a sub-panel dedicated strictly to the furnace. If the breaker is on the “off” position, the furnace cannot produce heat. Turn the breaker on. If it trips again, contact a professional for an inspection to see why it keeps tripping its electrical circuit.
Locate the furnace blower. On the blower, you will notice a status light. If the status light is red, press the reset button. If the reset button turns green, you will hear the furnace turn back on. If it goes right back to red, consult a professional.
Inspect the pilot light through the access hole. If the pilot goes out, it cannot burn the gas going to the boiler. If the pilot light is off, turn off the furnace and turn it back on to see if the pilot light ignites. If it does not ignite, consult the gas company to see if you have gas coming into your home. If the gas company confirms you have gas, the furnace has a faulty component that requires professional service.