Zone Valves
Three port Motorised Valves
A three port motorised valve has three connections, one from the boiler and then two others that divert the flow of water from the boiler, to either the hot water cylinder, the central heating radiators, or both at the same time (mid position). If you have a three port valve that diverts between hot water and heating, your radiators will not get hot whilst the hot water is in “demand”, this is called hot water priority.
Two port Motorised Valves
A Two Port Motorised Valve has 2 pipe connections, one from the boiler and the other going to the hot water cylinder or central heating radiators. Two port valves are generally known as zone valves, a central heating system will have a hot water zone valve and at least one heating zone valve, and larger homes should have more than one heating zone.