Why does my furnace run for only a few minutes then stop?

Your furnace running briefly then stopping is typically caused by overheating, which triggers the safety limit switch to shut down the system. This is a protective mechanism to prevent damage or dangerous conditions.

The most common culprit is a dirty air filter that's restricting airflow. When your furnace can't pull enough air across the heat exchanger, it overheats quickly and shuts down. Check your filter first - if it's clogged with dust and debris, replace it immediately. A severely dirty filter can cause this cycling pattern within just a few minutes of operation.

Other potential causes include blocked return air vents, closed supply registers throughout your home, or a malfunctioning blower motor that isn't moving air properly. In Ottawa's cold climate, even a partially blocked outdoor vent can cause similar issues with high-efficiency furnaces that use outdoor air for combustion.

More serious possibilities include a failing heat exchanger, faulty limit switch, or issues with the gas valve or ignition system. These require immediate professional attention, especially anything involving the heat exchanger, as this can create carbon monoxide risks. If you smell gas or notice any unusual odors, turn off your furnace immediately and call for emergency service.

Start with the simple fix - replace your air filter and ensure all vents are open and unobstructed. If the problem persists after these steps, it's time to call a licensed HVAC technician. In Ottawa's winter conditions, furnace issues need prompt attention to prevent system damage and ensure your family's safety. For reliable furnace repair service, Ottawa HVAC Pro offers emergency HVAC service to get your heating system running safely again.