The answer to 'why is my boiler not turning on' is that there are several common causes, including a tripped circuit breaker, low water level, thermostat issues, or a problem with the boiler itself. First, check the circuit breaker and reset it if it has tripped. Next, ensure the boiler has adequate water pressure - if the level is too low, the boiler may not turn on as a safety precaution. Then, check the thermostat to make sure it is set properly and calling for heat. If those basic troubleshooting steps don't resolve the issue, the problem may be with the boiler itself, such as a faulty ignition, control board, or other internal component.
If you're not comfortable diagnosing and repairing the boiler yourself, it's best to call in a professional HVAC technician. Boiler repairs can be complex and potentially dangerous if not done properly. A qualified technician can quickly identify the root cause and make the necessary repairs to get your boiler back up and running safely.