This larger differential is accomplished by lowering the burner off setpoint 3/8" below the casting line on ‘MD’ models when setting the burner on/off points at 150psi. This compensates for the narrowing of the setpoints at lower operating pressures (more pliable/less stiff bellows). The burner off point will move upward (closer to the casting line) at lower pressures.

For lower pressure applications (below 15psi operating pressure) you may want to consider using the Series 42 Pump Control/LWCO. The setpoints and differentials are less likely to drift as described because it is factory set at 50 psi. It is also available with fittings allowing it be connected to the boiler sight glass tappings.