Which of the following scenarios would require a temperature relief device?

A temperature relief device is specifically designed to prevent dangerous conditions in a hot water system. Its primary function is to release excess pressure and temperature that could otherwise lead to catastrophic failures, such as tank explosions.

When the hot water temperature exceeds safe limits, the pressure inside the tank can rise significantly. The relief device opens at a predetermined temperature (or pressure) to allow hot water and steam to escape, thereby reducing pressure and stabilizing the system. This is essential for maintaining safety and preventing accidents.

The other scenarios do not represent situations where a temperature relief device would be necessary. Heating cold water is a normal operation of water heaters, risks of contamination do not directly relate to temperature concerns, and lack of hot water availability indicates a different type of problem that isn't addressed through a temperature relief device.