The answer to 'why is my backflow preventer clogged' is that the backflow preventer can become clogged due to debris, mineral buildup, or other blockages in the device. This prevents the proper flow of water and can cause issues with your plumbing system.
Some common symptoms of a clogged backflow preventer include low water pressure, slow drainage, or even a complete blockage of water flow. To fix this, you'll need to inspect and clean the backflow preventer. This may involve disassembling the device and removing any debris or buildup. If the problem persists or you're not comfortable doing this yourself, it's best to call a professional plumber to diagnose and repair the issue.