When putting a cold boiler back in service, when should the vent be opened?

Opening the vent on a cold boiler as it is brought back into service is crucial to prevent the formation of a vacuum within the boiler. The correct practice is to keep the vent open until you reach a pressure of 25 psi. This allows any trapped air to escape while the boiler is being pressurized, which helps to ensure that steam can circulate freely once the pressure builds.

Maintaining pressure is vital for safe and efficient operations, as trapped air can create a barrier to the steam and lead to issues such as overheating, inefficient heating, or even physical damage to the boiler itself.

Other options suggest different timings for venting that do not align with the best practices for safe boiler operation. For instance, opening the vent when the boiler is warm may not ensure that air is expelled effectively during the initial pressurization stage. Opening the vent only when steam stop valves are open can also be counterproductive, especially if the boiler has not been adequately ventilated as it heats up. Lastly, stating that the vent should never be left open fails to acknowledge the necessity of proper air removal during startup to prevent operational hazards.