When is it necessary to perform a pressure test on a boiler?

Performing a pressure test on a boiler is critical after any significant repair or modification because this ensures the integrity and safety of the system following changes. Boilers are pressured vessels that operate under high-pressure conditions, and any alteration to their structure, such as welding or replacement of components, can affect their performance and safety. A pressure test validates that the boiler can withstand operational pressures without leaking or failing.

This procedure is not limited to just first installations or routine annual checks, which are important but serve different purposes. It's also essential to address immediate issues like leaks, but the pressure test specifically verifies that the entire system remains intact following any significant modifications. Therefore, option B correctly identifies when the necessity for a pressure test arises, emphasizing the need for safety and operational reliability in boiler systems.