The answer to 'why is my water softener slow draining' is that a clogged drain line or resin bed are the most common causes. Over time, mineral buildup, debris, or salt bridges can restrict the flow of water, leading to slow drainage from the softener. This can result in water backing up during the regeneration cycle.
To troubleshoot, first check the drain line for any kinks, clogs, or restrictions. You may need to clean or replace the line. Next, inspect the resin bed inside the softener tank - if it's compacted or covered in mineral buildup, you may need to clean or replace the resin. If the issue persists, the control valve or other internal components could be malfunctioning and may require professional repair or replacement.