An older furnace is more likely to need repairs in order to keep your home warm. The following are four common issues with older furnaces, along with tips for tracking down the cause of the problem.
1. Check for an Emergency Shut-Off
Many home furnace units are equipped with a shut-off switch. It may be a switch on the actual furnace that is clearly marked, or it could be as simple as a standard light switch placed on the wall or ceiling near the furnace. It's not uncommon for these switches to be flipped off, particularly those that resemble a standard light switch. Further, take a moment to check the circuit breaker switch for your furnace. Flip the breaker completely to the off position, and then flip it back on. A power surge, for example, can lead to the circuit flipping off.
2. Verify The Thermostat Setting
When a furnace seems to be heating poorly or just not turning on when it should, the first thing you should suspect is the thermostat. Start by turning the thermostat to the heat setting. Then, use a separate thermometer to determine the actual temperature of the room as read near the wall thermostat. Once you have the reading, turn the thermostat 5 degrees higher than the current room temperature. The furnace should pop on and run until it reaches the setting. If it doesn't, continue to adjust the thermostat upward until the furnace does come on. If the furnace eventually turns on, you may need a new thermostat. If it doesn't, then the issue may be with the furnace itself.
3. Test the Igniter Function
Proper igniter function is vital to ensure the fuel in the furnace is ignited so that heat can be produced. You can see the red glow of the igniter if you remove the furnace access panel, although you may need to dim the lights in the furnace room to make sure the glow is visible. Turn the thermostat setting 10 degrees or so higher than the current temperature and then check that the igniter is firing. If you don't see the glow, then you may need to have the igniter repaired or replaced.
4. Track the Heating Cycle
Premature shutoff is commonly the issue for a furnace that turns on but never seems to warm the home to the desired temperature. Turn your thermostat up and track the cycle from when the furnace pops on until it cycles off. If it cycles off before the desired temperature is reached, then your furnace isn't running a full cycle. Airflow can cause this issue, so make sure the filter is clean. Control board problems are another common cause, which will necessitate a repair.
If the above doesn't help you determine or fix the problem, contact a heating service in your area for more help.