A Printed Circuit Board, or PCB, is the control centre of the boiler. It controls every action within the appliance and can be found in most appliances from warm air units and fires to boilers. They are often referred to as a PCB, control box, mother board, driver board, sequence board, or power board. Conductive pathways are etched or "printed" onto board, connecting different components on the PCB, such as transistors, resistors, and integrated circuits. Certain appliances may have more than one PCB dependent on make and manufacturer.