Modern furnaces are designed to be as maintenance free as possible but furnace problems still occur occasionally.
(1) Check that the thermostat is working by turning it up a few degrees to see if the furnace kicks in.
(2) If it does you may need to either adjust the thermostat settings or clean out the air filters.
(3) Check that the pilot light has not blown out if the fuel is not igniting.
(4) If the furnace has electronic ignition the burners may need adjusting and this is best done by a professional.
Not Enough Heat
(5) Clean or change the air filters.
(6) If the burners still don’t provide enough heat they need adjusting by a professional
Furnace Turns on and off too Frequently
(7) Clean the air filters and check the thermostat settings.
(8) Make sure the blower motor is working efficiently and that the fan belt is not slipping.
(9) Make sure the blower motor is running smoothly and that the fan belt is not slipping (that could cause a squealing sound).
(10) If the noise is a rumble caused by the way the fuel is being burned, the burners need adjusting by a professional.
Smell of Gas
(11) If you have a gas furnace and you can smell gas this is definitely time to turn off the furnace, evacuate the house, and call in a professional. Never try to find and cure a gas leak for yourself.