The answer to 'why is my shut-off valve low water pressure' is that a partially closed or faulty shut-off valve can restrict the flow of water and reduce pressure. This is a common issue that can occur over time as the valve mechanism wears down or becomes stuck.
Some common symptoms of a shut-off valve causing low water pressure include reduced flow from faucets and appliances, difficulty flushing toilets, and inconsistent water pressure throughout your home. To fix the problem, you'll need to identify and inspect the shut-off valve, and either adjust it or replace it if necessary.