A forced-air furnace works by bringing in air, cleaning that air by passing it through a filter, heating the air, and then using the home's ductwork system to evenly and promptly disperse the heated air that will warm the home to the temperature you set the system to. Once the furnace has caused the air in the rooms to meet the setting, the system temporarily shuts off, only to come back on and repeat this process once the room temperature dips below the desired temperature again.
The air quality has gone downhill
The forced-air heating system is designed to improve the air quality while it warms the home. If you find your allergy symptoms are picking up or your breathing issues are getting worse, then the air quality in the home may be worse. This is an issue that you are going to want to check the air filter for to make sure it doesn't need to be replaced. If it's clean, then there's something else going on. This is also another issue where the ductwork may be the culprit. Over time, dirt and even more dangerous things like mold can accumulate, and in such a case, the system would need a professional cleaning.
The home never seems to get warm enough
Unfortunately, when you move into a home with an existing forced-heat furnace, you won't have any control over the size that was installed. If it's too small for the home, then you might find that it always seems to be chilly in your home, and it can feel drafty even when the system has just completed a cycle. A technician can let you know if this is the issue and install the proper size for your home.
The furnace is making noises you've never heard
It's never a good thing to start having a motor of any kind suddenly start making noises, and your forced-air furnace is no exception. If it starts being noisy, then this indicates any number of issues going on with the motor that you are going to need to have fixed.
The furnace won't turn on
If the furnace won't turn on, then you want to make sure it's getting power. Double-check the thermostat settings and/or check the fuse in the fuse box to make sure it's not tripped. If these things aren't causing the issue, then you need a technician to troubleshoot and then repair whatever is going on.
To learn more, contact a furnace repair service.