The answer to 'why is my water heater won't flush' is that there could be several common causes, such as a buildup of sediment, a faulty drain valve, or a blocked drain line. Symptoms may include difficulty draining the tank, slow water flow, or discolored water. Solutions can range from simple DIY flushing to more complex repairs that may require a professional plumber.
If you're comfortable doing basic maintenance, you can try flushing the water heater yourself. This involves attaching a garden hose to the drain valve, opening the valve, and letting the tank drain. However, if you encounter any issues or the water heater still won't flush properly, it's best to call a licensed plumber to diagnose and fix the problem. Attempting complex repairs without the proper skills and equipment can potentially lead to further damage or safety issues.