F-1 Liquid Inhibitor, 500ml. Protector F1 gives a long term protection of domestic central heating systems against internal corrosion and limescale formation. It prevents corrosion of all metals, copper and copper alloys and aluminium. It is suitable for all types of boilers, radiators and pipework systems. Fernox Protector F1 is compatible with all metals and materials commonly used in central heating systems.