Which boiler control setting is staggered to allow boilers to lead and lag?

• A. Calibration
• B. Overpressure
• C. Differential
• D. Hysteresis

Answer: (C)

Differential defines the on-off band for a boiler, i.e., how far the temperature (or demand) must move before the boiler changes state. By giving each boiler its own slightly different differential, you create offset turn-on and turn-off points. The lead boiler will start first and run until its set point plus its differential, then a lag boiler with its own offset will come online, sharing the load. This staggered sequence reduces simultaneous firing, smooths demand, and minimizes wear, making lead-lag operation practical and efficient. Calibration, overpressure, and hysteresis relate to accuracy, safety limits, and general cycling behavior, but the specific control that enables staggered, sequenced operation is the differential.