A boiler operating without adequate water may result in?

Operating a boiler without adequate water can lead to significant damage to the heat exchanger. The heat exchanger relies on sufficient water to absorb and transfer heat effectively. When water levels are low, the heat exchanger can become overheated, leading to thermal stress and potential failure of the materials. This overheating can cause warping, cracking, or even complete failure of the heat exchanger, which is a critical component of the boiler system.

In contrast, the other options imply positive outcomes or alternate scenarios that do not align with the consequences of low water levels. Increased efficiency would typically require optimal operating conditions, which are not present in low water scenarios. Emergency shutdowns are a safety protocol that may be initiated as a preventive measure, but they do not represent a direct result of the low water itself. Proper combustion relies on adequate water levels to maintain proper temperature and pressure, which are compromised when water is insufficient. Thus, the risk of damage to the heat exchanger is the most direct and critical consequence of inadequate water levels in a boiler.