The answer to 'why is my backflow preventer overflowing' is that the backflow preventer is likely clogged or malfunctioning, causing water to back up and overflow. This can happen due to debris buildup, mechanical issues, or a problem with the plumbing system. Backflow preventers are an important safety device that stops contaminated water from flowing back into your home's clean water supply, so it's important to address the issue promptly.
Some common causes of backflow preventer overflow include a broken or stuck check valve, a damaged diaphragm, or a blockage in the inlet or outlet pipes. If the backflow preventer is overflowing, it's best to call a licensed plumber to diagnose and repair the issue, as they have the specialized tools and expertise to properly inspect and service the device.