heating?

http://www.gasheating.co.uk/Mid-Position-Valve.html

Grey wire is Live When there is NO call for DHW
White wire is Live when there IS a call for CH

The Orange wire is Live whenever the boiler is asked to fire up - sometimes from the Boiler / Cylinder Stat / Programmer direction and sometimes from the direction of the Mid Position Valve Switches via programmer and Room Stat

Switched Live (please fire up) is conditioned by Pressure Switch and Overheat Stat

Peccavi
February 2010