When does the stack switch/primary control become active?

The stack switch, also known as a primary control, is designed to monitor the temperature within the flue or chimney. It becomes active when there is no heat in the chimney or smoke stack, which typically indicates that the burner is not operating efficiently or at all. This control is crucial for ensuring safe operation of the oil burner system.

By detecting a lack of heat, the stack switch can trigger necessary safety mechanisms to prevent potential hazards, such as the buildup of unburned fuel or fumes in the combustion chamber. This safety feature ensures that if combustion has not started or is insufficient, corrective actions can be taken before any dangerous situation arises.

Understanding the operation and role of the stack switch is important for maintenance and troubleshooting of oil burners since it plays a vital part in preventing unsafe conditions. In contrast, the other choices relate to operational conditions or maintenance actions that do not directly trigger the stack switch.