Under what circumstances is a post purge control required on a burner?

A post purge control is required on a burner when using a direct vent system. This control operates by removing combustion gases from the combustion chamber after the burner has been shut down, which helps to prevent the accumulation of hazardous gases. In direct vent systems, these gases can be expelled outside efficiently, but ensuring complete purging through a post purge function enhances safety by eliminating possible risks of backdraft or buildup of gases in the venting system, which could pose a hazard to occupants.

Additionally, while the other circumstances presented suggest various stages or conditions of oil heating systems, they do not necessitate the specific function of a post purge control in the same way that a direct vent system does. Maintaining gas safety and ensuring efficient operation is critical in direct vent applications, making the requirement for a post purge control in this scenario an essential safety measure.