Which type of pressure control in a heating boiler regulates maximum safe pressure?

The high limit cut-off is a crucial component in the pressure control system of a heating boiler. Its primary function is to ensure safety by preventing the boiler from exceeding its maximum operating pressure. When the pressure reaches a preset high limit, this control mechanism activates, shutting off the burner or other heat sources to stop further pressure buildup. This is vital because excessive pressure can lead to dangerous situations, including equipment failure or explosions.

In contrast, the other options serve different purposes in a heating system. Low limit cut-off ensures that the boiler does not fall below a certain pressure threshold, which is important for maintaining efficient operation and avoiding damage. Operating control refers to the regular monitoring and regulation of pressure within the desired range during normal operation. Emergency shut-off is a safety feature that can be activated in critical situations, but its function is broader and not specifically tied to maximum pressure regulation. Thus, the distinctive role of the high limit cut-off makes it the correct choice for regulating maximum safe pressure in a heating boiler.