

However, if the primary, or operating, control should fail, the high-limit control must operate, stopping the burner or other source of heat. The secondary device referenced above for both steam and hot-water boilers is referred to as a high-limit control and under normal conditions, would never be called upon to operate. A second device is used to prevent the boiler from exceeding the design temperature of an ASME BPV Code Section I boiler or the maximum water temperature indicated on an ASME BPV Code Section IV boiler nameplate.

Hot-water boilers require a device which senses water temperature and cycles the burner or other source of heat in order to maintain a consistent, predetermined operating temperature. A second device is used to prevent the boiler from exceeding the maximum allowable working pressure (MAWP) indicated on the boiler nameplate. Steam boilers require a device which senses steam pressure and cycles the burner or other source of heat in order to maintain a consistent, predetermined operating pressure.

Operating controls for boilers could be broadly defined to include burner management controls however, this inspector guide will be limited to the pressure and temperature operating controls required by the ASME BPV Code for steam and hot water boilers.
