The answer to 'why is my pressure regulator won't flush' is that the pressure regulator may be clogged or malfunctioning, preventing proper flushing. This can be caused by sediment buildup, mineral deposits, or mechanical issues within the regulator itself.
Common symptoms include low water pressure, irregular water flow, or the inability to fully flush the regulator. To resolve this, you may need to clean or replace the pressure regulator. This is generally a DIY-friendly task, but if you're not comfortable working with plumbing systems, it's best to call a professional plumber to diagnose and fix the issue.