When looking at a commercial boiler, I notice many controls are mounted on and around it. It reminds me of a Christmas tree with ornaments hanging from it. The function and duty of these controls are sometimes confusing.
The operating control is the main control for the boiler. This control will be set for the desired water temperature or steam pressure of the system. In most hydronic applications, the operating control will be set for 180° F. The industry has adopted 180° as the official design water temperature. Heating systems and equipment were designed to operate at full capacity using water at this temperature.
Be careful if the control is set for lower than 140° as the boiler flue gases would condense. Many manufacturers will void their warranty if the boiler water temperature is below 140°. When the flue gases condense, acids are released which will attack the piping, flue and chimney.
On steam systems, the operating control is typically set for 2 psi. The controls should be installed on a siphon or pigtail. This protects the control from live steam by using a water seal.
The operating control is an automatic reset-type control. That means the control will automatically start once the temperature or pressure drops to a predetermined temperature or pressure.