Name one way an expansion tank can become waterlogged?

An expansion tank can become waterlogged when air escapes past the upper gauge glass fitting, which disrupts the balance of air and water in the tank. The primary function of an expansion tank is to absorb the excess pressure produced by the thermal expansion of water as it heats. This is achieved by maintaining a specific air-to-water ratio in the tank.

When air escapes from the fitting, the volume of air that can cushion the water's expansion is reduced. This results in less air being available to absorb the pressure changes, causing the tank to fill with water and effectively become waterlogged. In this state, the expansion tank can no longer perform its function correctly, leading to potential issues within the boiler system, such as increased pressure or strain on pipes and fittings.

While other factors like pressure levels in the system can impact performance, they don't specifically describe the mechanism by which an expansion tank becomes waterlogged in the context provided. Thus, recognizing the relationship between the air compartment and the water level is crucial for understanding how an expansion tank maintains system balance.