The answer to 'heat pump freezing up' is that a frozen heat pump is a common issue that can be caused by several factors. This usually happens when the heat pump is not able to properly defrost, leading to ice buildup on the coils and preventing the system from functioning properly.
Some common causes of a frozen heat pump include low refrigerant levels, blocked airflow, malfunctioning defrost cycle, and extreme cold temperatures. Symptoms can include poor heating or cooling performance, ice buildup on the outdoor unit, and the system cycling on and off frequently. Solutions may involve cleaning the coils, adjusting the refrigerant charge, or repairing the defrost controls. In some cases, it's best to call a professional HVAC technician to diagnose and fix the issue.