Both of these have "3 Ports" ie inlet port and hw and heating outlet ports.
A mid position valve is able to allow water to flow to HW only,CH only and to both at once by holding the valve in the Mid Position,These valves normally have 5 wires. A 3 port diverter normally has 3 wires and can only supply CH on its own or HW on its own but not both together.These valves as such are interchangeable with some wiring alterations.
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