The answer to 'water heater not working' is that there are several common causes, including a faulty thermostat, sediment buildup, or a broken heating element. Symptoms may include no hot water, lukewarm water, or the water heater not turning on at all.
For minor issues like a tripped breaker or loose connections, you may be able to troubleshoot and fix the problem yourself. However, for more complex problems like a malfunctioning heating element or leaks, it's best to call a professional HVAC technician to diagnose and repair the issue properly.