A motorised valve is an electronically operated fitting that can control the flow of hot water throughout the central heating system such as to the radiators or taps. It is normally situated next to the hot water cylinder. There are two types of motorised valve used in domestic homes; a two port valve and a three port valve which are also known as a zone valve and mid position valve respectively. Port two valves are typically seen in on/off applications as the valve can be fully closed. This is a useful safety feature as allows for the complete shutdown of fluid flow in the case of an emergency. They can also vary the flow rate of fluids to alter pressure or temperature output. Port three valves have the same features as a port two valve however the additional port allows this fitting to mix fluids as well.