Which of the following is NOT typically a control found on heating boilers?

The emergency shut-off switch is actually a crucial safety component in heating boilers. It is designed to immediately turn off the boiler in case of an emergency, preventing potential hazards such as overheating or explosion.

In a typical setup for heating boilers, operating controls manage the day-to-day operations, ensuring the boiler maintains a specific temperature or pressure based on the needs of the system. High limit cut-off switches prevent the temperature from exceeding a safe level, while low limit cut-off switches ensure that the boiler does not operate when temperatures fall below a set threshold, thus protecting the system from damage and promoting efficiency.

Given this context, the emergency shut-off switch should be viewed as an essential safety feature rather than a control mechanism that operates under normal conditions. In fact, all the other options listed are standard operational controls that help in maintaining the proper functioning of the heating system during regular operation.