The boilers are drum-type with natural circulation, designed specifically to burn heavy oil. The pressure parts include the economiser, the drum, the down comer and the furnace wall tubes, the superheaters, the reheater and the attemperators for steam temperature control. The combustion air and flue gas system includes the force draft and gas recirculation fans, the air heaters for the heat recovery from the flue gases, air and gas ducts with relevant dampers.

The burners, of steam atomising type, are located in the front and rear walls of the furnace. The oil is heated to 90oC in a heater, using steam as the heating medium. This is secondary steam, generated in a reboiler to prevent the possibility of oil leakage pollution in the mainsteam/water system. In normal operating conditions, the primary steam for the reboiler and the atomising steam for the burners are extracted from the cold re-heat line. An auxiliary boiler which is common to the four units is used to provide heating steam for the oil in "cold start" conditions. Cold light oil can also be used for cold starts.

If the boiler needs to be re-fired shortly after a shut-down, there is the possibility of using primary steam from the main steam system so long as the pressure in the system has not fallen below 30kg/cm2(g).