Why is my heat pump not heating in winter?

Heat pumps can struggle or stop heating in winter due to several common issues, with outdoor temperature limits and defrost cycle problems being the most frequent culprits.

The most likely cause is that your heat pump has reached its heating capacity limit in cold weather. Standard air source heat pumps typically lose efficiency below -5°C and may struggle to provide adequate heat below -10°C. In Ottawa's harsh winters, this is a common issue with older or standard-efficiency heat pumps. When outdoor temperatures drop too low, the heat pump simply can't extract enough heat from the cold air to warm your home effectively.

Another frequent issue is defrost cycle problems. Heat pumps need to periodically defrost ice buildup on the outdoor coil, which temporarily reverses the heating process. If the defrost system isn't working properly, ice accumulation can block airflow and prevent heat transfer. You might notice thick ice or frost coating the outdoor unit that doesn't clear away.

Additional causes include dirty air filters restricting airflow, low refrigerant levels due to leaks, faulty thermostats, or issues with the backup heating system (if equipped). In Ottawa's climate, many heat pump installations include electric backup heat or a dual-fuel system with a gas furnace for extreme cold periods.

For safety and proper diagnosis, turn off the system if you notice unusual sounds, burning smells, or if ice buildup seems excessive. Check your air filter first - a clogged filter can cause the system to shut down on safety limits. If the outdoor unit is completely encased in ice, don't attempt to chip it away as this can damage the coils.

Your next step should be calling a licensed HVAC technician for diagnosis, especially since heat pump refrigerant systems require specialized tools and training to service safely. For a professional assessment of your heat pump's winter performance, request a quote from Ottawa HVAC Pro - we can determine if your system needs repair, maintenance, or if it's time to consider a cold-climate heat pump upgrade designed for Ottawa's winters.