The answer to 'why is my pressure regulator low water pressure' is that a faulty or improperly adjusted pressure regulator is the most common cause of low water pressure. The pressure regulator is responsible for reducing the incoming water pressure from the municipal supply to a safe level for your home's plumbing system. If the regulator is set too low or is malfunctioning, it can significantly restrict the flow of water and result in low pressure throughout your home.
Some common symptoms of a pressure regulator issue include low water pressure at all faucets, showers, and appliances, as well as frequent tripping of the pressure relief valve. To fix the problem, you may need to adjust the pressure regulator or replace it entirely if it is worn out or damaged. This is a job best left to a professional plumber, as improper adjustment or installation of the pressure regulator can lead to more serious problems like pipe bursts or water damage.