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
