My shower water temperature reaches what feels like an early plateau (warm enough to get in), but then continues to get warmer at the same handle position for the next 3-5 minutes. The obvious explanation would be that the cold pipes are initially keeping the temperature down, but this is the first place I've ever lived where I noticed this happening. Is it related to modern shower valves? Tankless water heaters? Or was I just slower to get in the shower for the previous 40 years?