The answer to 'water heater not turning on' is that there could be several common causes, such as a tripped circuit breaker, a faulty thermostat, sediment buildup, or a problem with the heating element. Symptoms may include no hot water, the water heater not heating up, or strange noises coming from the unit.
If the issue is a tripped circuit breaker or a simple reset of the thermostat, those are relatively easy DIY fixes. However, if the problem is with the heating element, sediment buildup, or a more complex issue, it's best to call a professional HVAC technician to diagnose and repair the water heater properly and safely.