The burner on a gas hydronic heating system is controlled by _____________.

• A. High limit control
• B. Thermostat
• C. Pressure switch
• D. Draft inducer

Answer: (A)

In a gas hydronic boiler, the burner is kept under control by the high limit safety device. Its job is to shut the burner off if the water temperature reaches a preset maximum, preventing overheating and potential damage. When the thermostat calls for heat, the burner may start, but the high limit monitor will interrupt the gas valve circuit if the water gets too hot. This safety interlock is what ultimately governs burner operation to protect the system. The thermostat provides the heat demand, but the high limit control ensures the burner can’t run beyond safe temperatures. The other components have different roles: the draft inducer moves exhausted gases, the pressure switch confirms proper venting pressure, and the thermostat signals the need for heat but doesn’t by itself shut the burner off for safety.