What is one sign of a defective pressure relief valve?

A continuous water leakage or discharge is a prominent indication of a defective pressure relief valve. This type of valve is designed to release pressure when it exceeds a certain threshold to prevent boiler damage or failure. If the valve is malfunctioning, it may not close properly after releasing excess pressure or may have become corroded or damaged, leading to a persistent leak.

In this context, other options do not directly signify a defect in the pressure relief valve. For instance, steam escaping from the boiler may indicate other issues, such as a malfunctioning boiler or improper operational conditions. Increased fuel consumption could suggest inefficiencies in the system, but it does not specifically point to the relief valve's condition. Similarly, reduced water pressure might be associated with various system problems, including issues unrelated to the pressure relief valve itself. Hence, the continuous leakage or discharge is the most definitive sign of a pressure relief valve that is not functioning correctly.