What causes a furnace to stop working in winter

Furnace failures in winter typically stem from a few common issues, with clogged air filters being the most frequent culprit. When your furnace stops working during Ottawa's harsh winters, it's usually due to restricted airflow, thermostat problems, or safety system shutdowns.

Clogged air filters are responsible for about 80% of furnace breakdowns. When filters become packed with dust, pet hair, and debris, airflow becomes restricted, causing the furnace to overheat and shut down as a safety measure. In Ottawa's dry winter air, filters can clog faster than expected, especially if you have pets or haven't changed the filter in 2-3 months.

Thermostat malfunctions are another leading cause, particularly with older thermostats that struggle in extreme cold. Dead batteries, incorrect settings, or a thermostat that's lost its programming can leave you without heat. Sometimes the issue is as simple as someone accidentally switching it to "cool" mode or the temperature being set too low.

Pilot light or ignition problems frequently occur during Ottawa's coldest snaps when temperatures drop below -20°C. Modern furnaces have electronic ignition systems that can fail, while older units may have pilot lights that get extinguished by drafts or component wear. Gas supply issues, though less common, can also prevent ignition.

Safety system shutdowns protect your family but leave you cold. High-limit switches trigger when the furnace overheats, flame sensors shut down the system if they can't detect proper combustion, and pressure switches stop operation if venting is blocked by snow or ice - common in Ottawa winters.

Never ignore a furnace shutdown - it could indicate a carbon monoxide risk or other safety hazard. While you can check the filter and thermostat settings yourself, gas appliance repairs require a TSSA-licensed technician. If your furnace won't restart after checking these basics, call for emergency service rather than repeatedly trying to restart the system.

For reliable furnace repair during Ottawa's winter emergencies, Ottawa HVAC Pro can put your request in front of Ottawa contractors the same day - ask each one what their after-hours rate is and whether they hold the TSSA certification the job needs.

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