The answer to 'heat pump not turning on' is that there are several common causes, including a tripped circuit breaker, a faulty thermostat, or issues with the compressor or other components. Symptoms may include the heat pump not starting up, no airflow, or the system not responding to the thermostat.
To troubleshoot, first check the circuit breaker and reset it if tripped. Next, inspect the thermostat to ensure it's set correctly and has working batteries. If those are not the issue, you may need to call a professional HVAC technician to diagnose and repair any problems with the compressor, refrigerant lines, or other internal components.