Which of the hydronic controls listed below de-energizes the main burner if the operating control fails in the closed position?

The high limit control is designed specifically to protect the hydronic heating system by monitoring the temperature of the water within the system. Its primary function is to de-energize the main burner if the water temperature exceeds a pre-set limit, which is indicative of a failure in the operating control that should typically regulate the burner operation. This safety feature is crucial to prevent overheating and potential damage to the system, as well as to ensure safe operation.

In contrast, low limit controls are used to maintain a minimum temperature to prevent freezing, while temperature and pressure relief valves serve to release excess pressure and prevent hazardous situations. Flow switches detect the movement of water through the system and are used primarily to ensure that water is circulating properly. While each of these controls plays an important role in the overall safety and efficiency of heating systems, the high limit control is specifically responsible for shutting down the burner in the event of an operating control failure that might lead to unsafe temperatures.