The answer to 'HVAC system not turning on' is that there could be several common causes, including a tripped circuit breaker, a faulty thermostat, or a problem with the HVAC unit itself. If your HVAC system is not turning on, the first thing to check is the circuit breaker to ensure it has not been tripped. If the breaker is fine, you should then check the thermostat to ensure it is set properly and functioning correctly. If the thermostat seems to be working, the issue may be with the HVAC unit itself, which could require professional diagnosis and repair.
If the issue is a simple tripped breaker or thermostat problem, you may be able to resolve it yourself. However, if the problem persists or you are unsure of the cause, it's best to call a licensed HVAC technician to inspect and diagnose the issue. They have the expertise and tools to properly identify and fix the problem, ensuring your HVAC system is running safely and efficiently.