The answer to 'why is my drain won't flush' is that there is likely a clog or blockage in the drain that is preventing proper water flow. Common causes include accumulated hair, soap scum, food particles, or other debris that has built up over time. This can cause the drain to become slow or completely blocked, preventing water from draining properly.
Some common symptoms of a clogged drain include slow draining water, gurgling sounds, or even water backing up into the sink or tub. In some cases, the drain may not flush at all.