The answer to 'furnace not turning on' is that there could be several common causes, such as a tripped circuit breaker, a faulty thermostat, or issues with the furnace itself. Symptoms may include the furnace not responding when the thermostat is adjusted, or the furnace making strange noises. Solutions can range from simple DIY troubleshooting to more complex repairs that require a professional HVAC technician.
If the furnace is not turning on, the first step is to check the circuit breaker and make sure it has not tripped. If the breaker is fine, the next step is to check the thermostat and ensure it is set to the 'heat' mode and the temperature is set higher than the current room temperature. If the thermostat appears to be working, the issue may be with the furnace itself, such as a faulty ignitor, blower motor, or other internal component. In these cases, it's best to call a professional HVAC technician to diagnose and repair the problem.