The answer to 'water heater no hot water' is that the most common causes are a faulty heating element, thermostat, or tank issues. Symptoms include lukewarm or no hot water, and the tank not heating up. Solutions may include replacing the heating element, adjusting the thermostat, or flushing the tank to remove sediment buildup.
If you're comfortable working on your water heater, you can try troubleshooting and making simple repairs yourself. However, for more complex issues or if you're not confident in your DIY skills, it's best to call a professional plumber. They can quickly diagnose the problem and make the necessary repairs to restore your hot water.