Malfunctioning Thermostat This is probably the most common problem, but also the least costly. If the thermostat is malfunctioning, it doesn't mean the heating unit is broken; it just means the heating unit doesn't know when to turn on. Filter Clogging This is a very common and cheap problem, and one that new homeowners find difficulty with. The filter, when clogged, won't let air pass so you'll get poor airflow through the household. If the furnace seems to work fine but you're not getting airflow, probably a bad filter. Fan Motor Malfunction This doesn't happen too often, but when it does, it most likely won't be noticeable at first. You can tell easily if the furnace feels warm but doesn't sound "on." You don't want to run the heater before getting it fixed, as this can cause overheating and damage to the unite. Pilot Malfunction or Disrepair This is a common problem that is easy to spot but requires immediate attention once you do spot it. The best way to tell is that the furnace is not warm or you detect (at all) the smell of gas. Turn off the gas and call someone to repair the problem right away. Electrical Issues If you've recently had a power outage, your furnace might not be broken at all. Sometimes an electrical storm or other irregularity can cause a fuse to bust in the circuit breaker. If this happens, you can test this by replacing the very cheap fuse and attempting to power up the furnace again. It should be noted that the above issues are mostly for forced air central heating and most likely won't apply to radiative heating or other sources. Remember that heaters are complicated machines, and people do go to school to learn to repair them. It's no shame calling someone for a repair, and it will most likely be a much safer affair. What this list does do is help you have a more educated conversation with a repairman as to avoid any extraneous charges.
