Unfortunately, you will not know if there is a problem with your furnace unless you need it to keep the house at a comfortable temperature. This often means that you are going to need to get in touch with the company that performs furnace services and request an emergency appointment. However, if you can do a bit of troubleshooting yourself, you may be able to do a quick fix yourself so that you don't need to pay for emergency services. Here are a few common problems you may find.
When the return air filter is clogged with dirt and dust, the furnace will not get the proper airflow to work efficiently. This will result in the unit coming on more frequently to keep your home warm, which will cost you extra money. In addition, the unit will work harder, pulling some of the dirt and dust into the internal parts of the furnace, causing damage that will need to be repaired by a professional. Go ahead and change or clean the filter, but be sure to have a technician come to do a routine inspection and maintenance.
If the thermostat is not working properly, the furnace will not know when it needs to turn on and shut back off. You can check this by adjusting the temperature both up and down on the thermostat and paying attention to when it comes on or shuts off. If you need to adjust the temperature so that it is not what you need -- such as setting it higher to turn on -- it is going to need replacing. If you have a bit of experience doing things around the house, you should be able to replace the piece yourself. However, if you feel in any way uncomfortable, ask a technician to come to do it.
The pilot light should be a nice blue color. If it is red or yellow it is not getting enough oxygen to properly burn the fuel. while it could be something as simple as a clog or too much of a draft, it is best to have a professional look things over. when you start messing with the ignition and pilot you could end up with fuel escaping and starting a fire.
Go ahead and try to determine what is wrong with your furnace when it seems to be running more than necessary, is using more fuel than normal, or is making weird sounds. However, unless you are certain you can take care of the issue yourself, contact a professional.