I know what 3 way/diverter/mid-position valves are with the motorised heads on but I am wondering about the diverter valves that contain a diaphragm and what the obvious differences are as to their use? (apart from looks)
I have read about how they work and understand this but what, when, where and why etc
Do systems use both?
Are 3 way only used if you have a hot water tank?

Any advice would be great

thanks as always.

A Diaphragm operated Diverter valve is commonly found on older Combi boilers, opening a hot tap causes a pressure drop across the diaphragm which results in the diverter valve shunting to the hot water port

A 3 port Mid position valve is an entirely diffrent unit, it is designed to be electrically controlled, and supply heat to either heating radiators or a hot water cylinder , or both.

Sometimes you will find an electrically operated Diverter valve on newer design Combi's A Diverter valve can only heat hot water or Heating one at a time, a Mid position valve can do as mentioned AND Both simultainously if required

You doing a plumbing course lol