The answer to 'why is my water heater not working' is that there could be several common causes, such as a faulty thermostat, a broken heating element, sediment buildup, or a tripped circuit breaker. Symptoms may include no hot water, lukewarm water, or strange noises coming from the tank.
If the water heater is not producing any hot water, the first step is to check the circuit breaker or fuse to ensure power is being supplied. If the power is on, you can try resetting the thermostat or checking the heating element. Sediment buildup can also prevent the water heater from heating properly, so you may need to flush the tank. However, for more complex issues or if you're not comfortable working with electrical or plumbing systems, it's best to call a professional HVAC technician to diagnose and repair the problem.