The answer to 'why is my pressure regulator frozen' is that the pressure regulator has likely frozen due to extremely cold temperatures. Pressure regulators are designed to maintain a consistent water pressure in your home's plumbing system, but when exposed to freezing temperatures, the internal components can freeze and prevent the regulator from functioning properly.
Some common symptoms of a frozen pressure regulator include low water pressure, no water flow, or the regulator feeling very cold to the touch. If the regulator is frozen, it's important not to try to thaw it yourself, as this can damage the internal components. Instead, you should call a professional plumber who can safely and properly address the issue.