How to Troubleshoot a Furnace: 7 Steps to Finding a Solution

During cold winter temperatures, a well-running furnace is essential to maintaining comfort in your home. Regular maintenance on your HVAC system helps ensure optimal performance on the coldest days when you need it most. 

Unfortunately, unexpected furnace problems can arise. If you’re having trouble with your heating system, review the following steps suggested by our Enercare furnace expert to identify a possible solution. 

1. Inspect the Thermostat

When your home isn’t heating properly, the first and easiest place to start is the thermostat. The thermostat measures its surrounding indoor air temperature to control when the furnace turns on or off. When your thermostat is configured incorrectly, it can lead to your furnace malfunctioning. 

First, your furnace won’t run if the thermostat isn’t on. If your thermostat approach is to set-it-and-forget-it,  simply checking the thermostat batteries, if it’s not a wired unit, may solve the problem. 

Next, if your thermostat controls your furnace and central air conditioning, it will have a Heat and Cool setting. Ensure that your thermostat is set to Heat. 

Additionally, review which temperature you set the thermostat to. The thermostat does not activate the furnace to generate heat unless the temperature setting is higher than room temperature. 

If the temperature in your home feels consistently different from the thermostat setting, your thermostat may be poorly placed. If it is too close to alternative heat sources or exterior doors, it can impact the thermostat’s temperature reading and subsequently result in heating problems. If you think this may be the case, contact a technician to evaluate your thermostat location. 

Lastly, if you have updated your home with a smart thermostat, it is essential to inspect the device for any wireless connection or software glitches. Manually restarting the device to get it back online can troubleshoot this problem. 

If you have an older HVAC system that doesn’t have a common “C” wire, your smart thermostat “steals” power from the system’s existing circuits. Sometimes, this can cause your system to malfunction. Additionally, the batteries of the thermostat will be shortened if there is no common wire.

Hiring a technician to install a “C” wire can resolve this problem. 

2. Change the Furnace Filter

Because many homeowners forget to clean their furnace filters, our furnace expert says a clogged filter can be the most common cause of furnace malfunction. A dirty filter can be compared to breathing with a hand over your mouth. The dirt prevents smooth airflow and subsequent heat output. 

To check your furnace filter, turn off the thermostat and furnace and remove the filter, typically located on the side of the furnace. Our expert recommends holding the filter up to a light source. If light cannot pass through, the filter is too dirty and needs replacing. 

At a minimum, our expert suggests replacing the furnace filter twice annually–at the beginning and end of the cold weather season. However, purchasing a new filter more frequently, as often as every three months, is recommended.

3. Confirm the Furnace Is Getting Power

There is a main switch on every furnace. Check to make sure yours is switched “on.” Furnace switches usually look like light switches on the wall near the furnace. Once it switches on, wait a few minutes, as some furnaces slightly delay turning on. If the furnace doesn’t turn on, you may need to contact a professional to investigate the electrical source. 

4. Make Sure the Circuit Breaker Isn’t Tripped

If the furnace switch is on, but the furnace still isn’t generating heat, the circuit breaker feeding its power may be tripped. Check the breaker box to see if the HVAC breaker is on. 

Typically, the breaker box is labeled correctly. If it isn’t, the furnace breaker may be the toggle switched in the opposite direction of the rest. If you’re still having trouble identifying the furnace breaker, our expert suggests flipping on each breaker until you hear the furnace turn off, indicating that you’ve found the furnace breaker.  

To reset the furnace breaker, switch it off and back on. Afterward, label the furnace breaker. 

5. Check the Vents for Blockage

Inspect all the vents and registers around your home to ensure they are open and unobstructed. Large furniture or a rug covering the register restricts heat flow from the air vents and throughout your home. 

If your furnace intakes air from outdoor vents, inspect the area around the external intake and exhaust. Dirt, leaves, and snow can accumulate around them and prevent necessary air intake for the furnace. Keep this area free of debris during the heating season.

6. Make Sure the Front Panel Door Is Secure

If the furnace’s front panel door isn’t completely closed, it will trigger a safety switch that prevents the unit from operating. Inspect the panel door to make sure it is securely closed.  

7. Call a Professional

If you’ve tried each troubleshooting step and couldn’t determine why your furnace isn’t working, it’s time to contact a professional. A hired technician has the expertise to navigate your furnace system and check for any part deterioration or malfunction in the electric panel, burners, gas valve, and more. 

If you’re a homeowner in Ontario, select the button below to schedule a repair service with one of Enercare’s trusted technicians. You may also choose to sign up for Enercare’s furnace maintenance plan to help extend the life of your furnace and prevent future equipment breakdowns.