The answer to 'water heater not heating' is that there are several common causes, including a faulty thermostat, sediment buildup, or a broken heating element. Symptoms may include lukewarm or no hot water, and the water heater not kicking on. Solutions can range from simple DIY fixes to calling a professional HVAC technician, depending on the issue.
For example, a tripped circuit breaker or loose wiring connection may be an easy DIY fix, while a failed heating element or leaking tank would likely require a professional repair. It's important to diagnose the root cause to determine the appropriate solution.