The answer to 'why is my pressure regulator constantly running' is that the pressure regulator is likely faulty or malfunctioning. A pressure regulator is designed to maintain a consistent water pressure in your home, but if it is constantly running, it indicates an issue with the regulator itself.
Some common causes of a constantly running pressure regulator include a worn-out diaphragm, a stuck valve, or a problem with the spring mechanism. This can lead to fluctuating water pressure, water hammer, and increased wear on your plumbing system. If the pressure regulator is not functioning properly, it's important to have it repaired or replaced to prevent further damage.