Which valve should be checked first if a boiler is experiencing abnormal water levels?

When a boiler is experiencing abnormal water levels, checking the gauge glass valve first is crucial because it directly reflects the boiler's water level. The gauge glass is designed to provide an accurate visual indication of the water level within the boiler. If there is an issue with the gauge glass valve, such as it being stuck or malfunctioning, it may give a false reading, leading to incorrect assessments of the water level.

Obtaining accurate information from the gauge glass is vital since it informs decisions that affect the safety and efficiency of the boiler's operation. If the gauge glass valve is not functioning properly, it could lead to either an over-filling or under-filling scenario, both of which can have serious implications for boiler operation. Therefore, ensuring the gauge glass valve is operational helps determine if the issue lies within the water level measurement itself or if further investigation is needed with other components such as the feedwater valve or other safety devices.