Tempering valve
A mixing valve that blends in cold water so tap water can't scald, even when the tank runs hotter.
A tempering valve — also called a thermostatic mixing valve or anti-scald valve — sits on the water heater's hot outlet and automatically blends in cold water to cap the temperature delivered to your taps (typically around 120°F) regardless of how hot the tank itself runs. It exists to solve a real trade-off: storing water hotter (around 140°F) suppresses Legionella bacteria and stretches your hot-water supply, but 140°F water can cause a third-degree burn in about five seconds — dangerous for young children and older adults. A tempering valve lets you store hot and deliver safe. Many newer codes require one. It's a clean fix for anyone who can't simply turn the tank down, and a core part of a [new-home safety check](/guides/how-to-childproof-and-safety-check-a-new-home).