Mid-position Valve Wiring

[Paulhar]

Hi All,

I've searched the forum for an answer to this without luck so here goes . . .

I've just replaced a Vitodens 100 system boiler with a Baxi Megaflow system boiler which is connected to an existing unvented cylinder.
I've had to fit a new 3 port valve but I'm hoping to keep the existing cylinder stat which is a Codice and has two wires emerging from it. Unfortunately all the wiring diagrams I can find assume 3 connections on the stat. As a result the grey wire on the mid-position valve (which normally connects to the Cyl Stat 'Satisfied' terminal) has nothing to connect to.
The weird part is that the hot water side of things appears to work fine but the heating doesn't fire the boiler up at all. Does anyone know if the grey on the valve not being connected could scupper the heating.
If anyone has a wiring diagram for the Codice stat or for the inside of a Corgi (Honeywell Compatible) mid-position valve I'd be grateful.

 

[buckley plumb]

On an unvented cylinder if it's got a 3 port it should have a 2 port aswell to stop heat to cylinder coil. Basic g3 requirement. Do you have unvented ticket if not don't touch due to safety issues

 

[ShaunCorbs]

+1 to the above and why you change boilers?

 

[Dotty]

Job 38.11