The answer to 'why is my water softener won't flush' is that there are several common causes, including a clogged or malfunctioning drain line, a problem with the control valve, or a buildup of minerals in the system. Symptoms may include the softener not cycling through the regeneration process properly, water backing up, or the system not flushing effectively.
Some potential solutions include checking the drain line for blockages, cleaning or replacing the control valve, and performing a manual regeneration cycle to clear any mineral buildup. If the issue persists, it's best to call a professional plumber, as water softener repairs often require specialized knowledge and equipment.