The answer to 'water heater not working' is that there could be several common causes, including a faulty thermostat, a broken heating element, sediment buildup, or a leak. Symptoms may include no hot water, lukewarm water, or water leaking from the tank. Solutions can range from simple DIY fixes to calling a professional HVAC technician, depending on the issue.
If the water heater isn't producing any hot water at all, the problem is likely a faulty thermostat or heating element. These are relatively easy DIY repairs if you have some basic plumbing skills. However, if you're not comfortable working on the electrical components, it's best to call in a professional HVAC technician to diagnose and fix the issue.