Abstract: A boiler is provided with: a boiler body in which the water level inside water pipes when combustion by a burner is stopped is lower than the upper ends of the water pipes; water supply means; control means which controls the water supply means depending on the water level in the boiler body; header water level detection means which detects a water level existing inside an upper header; and a downcast pipe. The control means performs first control for controlling the water supply means so as to lower a boiler body water level when the water level detected by the header water level detection means reaches a header set water level and second control for controlling the water supply means so as to raise the boiler body water level when the amount of drop in the boiler body water level reaches a predetermined amount after the first control.

Abstract: The boiler is provided with: a boiler body in which the water level inside water pipes when combustion is stopped is lower than the upper ends of the water pipes; external water level detection means which communicates with upper and lower headers and detects a boiler body external water level; control means which controls the water supply means so as to lower the water level inside the boiler body when the water level detected by the external water level detection means reaches a first set water level; and header water level detection means which detects a water level existing inside the upper header by boiler water being pushed up by air bubbles. The control means controls the water supply means so as to lower the water level inside the boiler body when the water level detected by the header water level detection means reaches a second set water level.

Abstract: A boiler system has a boiler and a combustion amount control unit. The boiler includes a boiler body, a discharge unit, a discharge passage, a feedwater preheater and a feedwater temperature measuring unit. The feedwater preheater includes a heat exchanger. The feedwater temperature measuring unit measures a feedwater temperature that is the temperature of the feedwater flowing in the heat exchanger. The combustion amount control unit controls combustion amount in the boiler, and has a feedwater temperature threshold as a threshold relating to the feedwater temperature. The combustion amount control unit minimizes the combustion amount in the boiler in a case where the feedwater temperature measured by the feedwater temperature measuring unit is the feedwater temperature threshold or lower.

Abstract: A boiler system has a boiler and a combustion amount control unit. The boiler includes a boiler body, a discharge unit, a discharge passage, a feedwater preheater and a feedwater temperature measuring unit. The feedwater preheater includes a heat exchanger. The feedwater temperature measuring unit measures a feedwater temperature that is the temperature of the feedwater flowing in the heat exchanger. The combustion amount control unit controls combustion amount in the boiler, and has a feedwater temperature threshold as a threshold relating to the feedwater temperature. The combustion amount control unit minimizes the combustion amount in the boiler in a case where the feedwater temperature measured by the feedwater temperature measuring unit is the feedwater temperature threshold or lower.

Abstract: Boiler efficiency is further improved and the whole boiler body is slimmed down by totally improving heat transfer surfaces confronting gas flow passages, i.e., by forming the heat transfer surface structure into three stages, and moreover by making effective use of the whole heat transfer surfaces of water tubes equipped with fully circumferentially finned water tubes.