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Most homes in Toronto have a very reliable heating system. But sometimes, it is unavoidable to meet unfortunate circumstances such as a furnace breakdown. We know how frustrating it is when your heating buddy suddenly fails. And while there is no one answer to “what can cause a furnace to stop working?” having a thorough understanding of the possible reasons will help you understand further.

Below we listed some of the most common issues that might trigger your furnace to stop operating. While there are several tips and tricks to avoid and amend them, we highly recommend seeking professional help for some complicated issues.

Your air filters are clogged.

If you are trying to determine what can cause a furnace to stop working, look at your air filters. While it is easy to disregard them, the problems they bring about could be far worse. 

Dirt build-up will be evident if you haven’t cleaned or replaced your air filters regularly as recommended. It could trigger a restricted airflow that limits air intake into the heat exchanger. Once the heat exchanger receives little air, heat builds up and triggers system malfunction because of the overheating. To avoid this, replace your filters regularly or clean them as needed. 

Your thermostat is not on.

Your thermostat is the master of operation of your furnace. It might be a potential answer to, “what can cause a furnace to stop working?”

If your furnace stops operating, inspect if your thermostat’s power is on. Since it communicates the furnace’s power on and off, it might be a factor as to why the heating system stops working. If it is on, but your furnace is still off, try to look at the settings and adjust it. You have to ensure that the heat mode settings have a few degrees above the indoor temperature to initiate heating. If you notice that your thermostat is off or is glitching, it might be the batteries needing replacement. 

You have a cracked heat exchanger.

The furnace’s heat exchanger is one of the most vital components of the system. If you’re still figuring out what can cause a furnace to stop working, it might be behind this. 

Heat exchanger functions in its literal translation: exchanging heat from the combustion to the airflow. It is usual to bear cracks as it wears and tears over time with constant use. These cracks can cause your furnace to gobble up more energy as it functions and even leads to carbon monoxide poisoning if unaddressed. Because it is a high risk to your safety, you must call a professional immediately. Carbon monoxide leaks could impose severe dangers to your health, so immediate attention to this issue is required.


What can cause a furnace to stop working? It is not effortless to determine these due to the boundless possibilities present. Your heating system has a complex component structure which could bear anomalies that trigger such malfunction. It is always best to have a technician diagnose any problems. You will be at peace knowing they are experts in what they do and will help prolong the lifespan of your furnace. 

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