Which device in an oil burner closes its contacts when the temperature of the fuel pipe rises?

The stack switch or relay is a critical safety device in an oil burner system. Its primary function is to monitor the temperature of the flue gases; when these gases reach a certain temperature due to combustion processes, the stack switch activates and closes its contacts. This action signals the oil burner to operate or to shut down if necessary, thereby preventing dangerous overheating that could lead to a fire or other hazardous situations.

With this thermal monitoring, the stack switch helps ensure that the oil burner operates efficiently while protecting the overall system from potential harm. It is an essential part of the safety interlock mechanisms that maintain the safe operation of heating appliances.

In contrast, the ignition transformer is responsible for supplying the high voltage needed to ignite the fuel-air mixture in the combustion chamber but is not temperature-sensitive. The booster pump is used to increase fuel pressure in the system, ensuring that fuel is delivered effectively to the burner, but it does not monitor temperatures. The fuel line filter serves to remove impurities from the fuel oil before it reaches the burner, which is vital for performance but unrelated to temperature control.