Most heat pumps made in the last 2 decades are computer controlled with a wide array of temp and pressure sensors. Stuck reversing valves do happen, but it's li

Most heat pumps made in the last 2 decades are computer controlled with a wide array of temp and pressure sensors. Stuck reversing valves do happen, but it's likely the unit will shut down due to an ambient outdoor temp, cool temps, or refrigerant pressures that are too high for heating mode. Not much different from a gas furnace. If somehow the computerized safety controls went bad and the unit ran without the blower fan, it would quickly overheat and destroy itself and possibly catch the house on fire. Luckily, these failsafe systems are well engineered with multiple redundancies. They aren't hacked together React apps.