Which of the following could be a consequence of setting the ECO too high in a residential water heater?

Setting the ECO (energy cut-off) too high in a residential water heater can indeed lead to a significant risk of burns and scalding. The ECO is designed to prevent the water from reaching excessively high temperatures that could be dangerous for users. When the ECO setting is elevated, the water temperature can exceed safe levels, increasing the likelihood of thermal injuries when users interact with the hot water supply.

The other consequences associated with the ECO being set too high would not typically manifest in the same way. For instance, an increase in energy efficiency or improved heating speed would not result from this adjustment; the heater might use more energy due to excessive heating cycles, leading to inefficiencies rather than improvements. Similarly, while a reduced lifespan of the heater could potentially occur from consistently operating at higher temperatures, the immediate and most critical consequence is the heightened risk of scalding injuries.