"Some of the common problems faced by gas furnaces are the following: Lack of maintenance: In case, one fails to schedule maintenance of the gas furnace at regular intervals there are chances that the furnace stops working and some of its parts might breakdown. Dirty filters: When the filters of a gas furnace is dirty, it has to work harder to continue with similar kind of airflow. As a result there is higher wear and tear of the machine. Malfunctioning thermostat: If the thermostat of the furnace is faulty there might be problems with the fan or the comfort level. Frequent cycling: When the furnace frequently cycles between “on” and “off”, it indicates that a dirty filter, improper airflow, and a bad thermostat setting. Besides these there are a few other problems that might trouble a gas furnace. However, there are ways to repair gas furnaces even before you get in touch with an expert HVAC technician. Some of the ways that one can put to use in order to repair gas furnace include the following: Change the air filters: It has already been mentioned that dirty air filters cause a lot of problems in the functionality of gas furnaces. Hence, it is important that filters are cleaned at least once in a month and they will have to be replaced as and when required. Check the thermostat: Many of the times it is seen that by replacing the batteries of the thermostat makes it functional once again. So you can try changing the batteries. When the furnace cycles too frequently, you might have to check the setting of the fan. It should always be in the ‘Auto’ mode. Similarly, if the thermostat do not produce enough heat, you will have to check the thermostat whether it is in the ‘Heating’ mode or not, if not you will have to set it at the heating mode and ensure that the temperature is set a level that is higher than the room temperature. "