How do I distinguish between a minor, normal pressure drop and a significant leak when dealing with E119?

A minor pressure drop (e.g., 0.1-0.2 bar over several weeks) is often normal, caused by the release of small amounts of air or system cooling. A significant leak is indicated by a rapid and consistent drop in pressure within a few hours or days after repressurizing, or visible signs of water around pipes, radiators, or the boiler itself. If you find yourself needing to repressurize frequently, it's a strong indicator of a significant issue.