Thanks all! its a 3 port mid position valve fitted.How can i tell if its "S" or "Y" plan just by looking cheers.
3 Port Mid position valve is a 'Y' plan..
This is the one where you can get what appears to be unexpected voltages at the cylinder stat..
As you say earlier..
'C' on your cylinder stat is the 230v trigger from the programmer 'Water ON'
'1' on your cylinder stat is the 230v output to fire the boiler while the water is cool.
'2' on on your cylinder stat is the 230v output to the Grey wire on the valve to position it all the way over for heating only, while the water is hot.
The first confusing bit comes because you get 230v on '2' when the Hot water is switched off at the programmer;
This is because 230v is needed on the grey wire as stated above..
(and the grey is common to '2' on the cylinder stand AND the water OFF at the programmer.)
The second confusing bit comes because you get 230v on '1' when the Hot water is switched off at the programmer and the heating is switched on.
This is because 230v is fed via the orange on the valve to the boiler..
and the orange is common to '1' on the cylinder stat AND the boiler live trigger.
So it is possible to be getting 230v reading with respect to earth in a varied bunch of situations NOT just your water on/off requests..
The Honeywell drawings are in the downloads section..
If you look at the ones for the 'y' plan it "hopefully" will make more sense!
:Salute