Heat pump not heating in cold weather: what is normal and what needs service?
How to describe a cold-weather heat-pump problem, including defrost behaviour, backup heat and signs that justify a repair request.
Updated September 28, 2026Cold-weather performance is a system question, not only an outdoor-temperature question
Modern heat pumps vary widely by model and climate rating. A cold snap does not automatically mean failure, but a system that cannot maintain temperature, repeatedly faults or develops abnormal ice may need service.
Defrost cycles can look unusual
During defrost, outdoor-unit behaviour changes temporarily and visible vapour can occur. What matters is whether the unit returns to normal heating and whether ice clears as designed. Persistent heavy ice, repeated shutdowns or no recovery after defrost are more useful service clues.
Send model and symptom details
Provide the outdoor temperature, indoor setpoint and actual temperature, model number if accessible, thermostat alerts, whether backup or auxiliary heat is operating, and photos of unusual outdoor-unit icing. That helps a technician distinguish a control issue from a performance or mechanical problem.