The answer to 'why is my heat pump freezing up' is that a heat pump can freeze up due to a variety of reasons, including low refrigerant levels, airflow issues, or problems with the defrost cycle. When a heat pump freezes, it can reduce heating efficiency and even cause the system to shut down completely.
Some common causes of a freezing heat pump include low refrigerant levels, a dirty air filter restricting airflow, a malfunctioning defrost cycle, or issues with the outdoor coil. Symptoms may include ice buildup on the outdoor unit, reduced airflow, and poor heating performance. To fix a freezing heat pump, you may need to recharge the refrigerant, clean the air filter, or reset the defrost cycle. If the issue persists, it's best to call a professional HVAC technician to diagnose and repair the problem.