What should be checked to ensure the proper functioning of a water heater?

Ensuring the proper functioning of a water heater involves several important factors, one of which is the presence of a drain valve. The drain valve is crucial as it allows for the periodic maintenance of the tank, including flushing out sediment and minerals that can accumulate over time. This maintenance is essential for the longevity and efficiency of the water heater. A functioning drain valve also helps in preventing over-pressurization and potential leaks, thus contributing to the overall safety of the unit.

In contrast, while the color of the tank and the type of insulation used can provide some indication of the unit's construction and energy efficiency, they are not direct indicators of functionality. The age of the water heater is relevant for understanding its condition and potential lifespan but does not directly impact its operational capability at any given moment. Therefore, checking for a drain valve is the most immediate and relevant factor in evaluating whether a water heater is functioning properly.