Feed water pumps run intermittently and are controlled by a float switch or other similar level-sensing device energizing the pump when it detects a lowered liquid level in the boiler. The pump runs until the level of liquid in the boiler is substantially increased. Some pumps contain a two-stage switch. As liquid lowers to the trigger point of the first stage, the pump is activated. If the liquid continues to drop, the second stage will be triggered. This stage may switch off the boiler equipment preventing the boiler from running dry and overheating by triggering an alarm. The feed water pumps take a suction from both the condensate and heater drains systems. These pumps raise the pressure to about 425-450 psi.