Labor Day may be the unofficial end of summer and the autumnal equinox the official end, but for many of us in colder climates the true end of summer that we feel in our bones happens whenever we first turn on the furnace for another year. Other than that initial tinge of sadness (or maybe happiness) at the acknowledgement that winter is not far off, as long as the furnace kicks on the way it's supposed to, there's no need to give it another thought. But what about when the furnace doesn't work?

Here is a list of common home heating problems and how to handle them.

1. Furnace Blows Cold Air

Check to make sure the thermostat is set to AUTO instead of ON. The ON setting keeps the blower working continuously, even when the furnace is not producing heat.

If your furnace goes from blowing hot air to blowing cold air, but then no air at all, the most likely cause is overheating. The limit switch, a safety device, turns the furnace burners off when they get too hot. The blower keeps blowing cool air until the furnace temperature returns to a safe level.

A furnace overheats when the air filter gets dirty and clogged, preventing the flow of fresh air through the HVAC system. Replacing the air filter every 30-60 days keeps the furnace running efficiently, prevents excessive wear and tear and keeps the furnace from overheating. Repeated overheating will damage the heat exchanger, which is an expensive repair. Air filters, on the other hand, are quite inexpensive and replacing them regularly is a simple maintenance task that will save money on energy costs as well as repair and replacement costs.

Another reason a gas furnace may be blowing cold air is that the pilot light is out. Try relighting it. If it doesn't light, make sure the gas is flowing to the furnace. The gas valve is in the ON position when it is in line with the gas supply pipe. If that doesn't work, the pilot light may be in need of cleaning. If the pilot light doesn't stay lit, the thermocouple needs to be adjusted or replaced.

2. Furnace Makes Noises

Some furnace noises—the sound of the furnace kicking on or the fan blowing, even small pops in the air ducts—are quite normal and, in general, are easily and safely ignored. Loud, unusual and persistent noises, however, could signal a serious problem and should be checked by a certified technician.

Loud scraping that sounds like metal on metal indicates a problem with the blower wheel. The blower wheel may be broken and in need of repair. If it is merely loose and hitting the blower casing, a technician can tighten the wheel so that it is secure. The most serious cause is a broken motor mount that allows the blower assembly to drop and make contact with the housing.

A loud bang or pop when the furnace turns on could be caused by dirty furnace burners. If you hear this sound repeatedly, call for service. Debris prevents the burners from igniting right away, but gas accumulates during that delay. The bang is the sound of all that gas finally igniting. These tiny explosions can crack the heat exchanger.

The popping noise is also common with metal air ducts, which expand and contract when the blower turns on and off. This often occurs if the ducts are too small or are not sturdy enough, if vents are closed or if the air filter is clogged.

A squealing or whining noise can result from a damaged or slipping blower belt, shaft bearings that need lubrication or a malfunctioning blower motor. Each of these requires a technician to make the repair or replace the part.

3. Furnace Smells Strange

The first time you turn on your furnace for the season, you may notice an unpleasant musty smell. It is likely caused by a build-up of dust and should dissipate quickly. If it doesn't go away after a day or so, however, try changing the air filter. If the musty, burning smell persists, contact your HVAC technician for assistance.

More serious is a metallic or electrical smell or a smell of burning oil, hot plastic or rubber that could indicate components of your furnace are overheating. In this case, turn the furnace off and unplug it immediately. Call for a professional inspection and periodically check on the equipment until a technician can evaluate it.

Another dangerous smell is one of rotten eggs. The scent of rotten eggs or sulfur is added to natural gas as a safety precaution to help detect leaks. Gas leaks can lead to an explosion, so if you suspect one, leave your home immediately. Wait until you are a safe distance from your home to call the fire department or utility company to report the leak.

4. Thermostat Isn't Working

A problem with your heat could actually be a faulty thermostat, rather than the furnace itself. Here are a few things to check.

Is the thermostat set correctly? The settings of both mechanical and electronic thermostats can be inadvertently changed. Make sure yours is set or programmed correctly.

Is the thermostat in a good location? Proximity to a lamp or other heat source, even direct sun, as well as drafts or placement on an exterior wall can cause the thermostat to misread the temperature in the home. If this is the case, relocate the thermostat to an interior wall away from heat and drafts.

Is the thermostat dirty? Dirt can collect in older, mechanical thermostats and affect function. Use a can of compressed air to clean it, and clean the contacts by gently sliding a piece of paper in between.

Is the furnace cycling too frequently or infrequently? The anticipator in the thermostat (the flat metal pointer inside) can be adjusted to correct this. Move the pointer slightly higher to increase the frequency, or slightly lower to decrease the frequency.

Additionally, you can replace old batteries with fresh ones, calibrate the thermostat with a thermometer to make sure it is registering the correct temperature and check the wiring to make sure all connections are secure. (Turn the power off before checking or adjusting wires.)

HVAC technicians recommend having your system professionally serviced annually. This may even be required by the manufacturer to keep the warranty in effect. A proper maintenance check includes a thorough cleaning and inspection of all the components. Trained technicians can spot minor problems before they become major ones, preventing inconvenient breakdowns and expensive repairs. Regular maintenance also prolongs the life of your system and improves efficiency.