What are some of the functions of combustion controls during burner operation?

Combustion controls play a crucial role in ensuring that the burner operates efficiently and safely. The functions mentioned under the correct choice include pre-purge, maintaining the appropriate air-to-fuel ratio, and post-purge processes.

Pre-purge is essential to clear any combustible gases that may have accumulated in the burner before ignition, reducing the risk of explosions. The air-to-fuel ratio is vital for efficient combustion; if this ratio is too rich in fuel or too lean in air, it can lead to incomplete combustion, increased emissions, and potential safety hazards. After the burner has completed its cycle, post-purge helps to clear the combustion chamber of residual gases, which also reduces the risk of an explosive mixture being present for the next start.

Considering the other choices, monitoring water levels pertains to boiler operation and safety but is not a direct function of combustion controls. Adjusting pressure relief valves does relate to safety but is a separate function from the control of the combustion process itself. Controlling circulating pumps is important for maintaining water circulation in systems such as boilers but does not involve the combustion phase directly.