I wonder if any one can help, I need advise on how to wire a vaillant Ecotec Plus 630 system boiler to a Honeywell Y plan so that the y plan switches the boiler on independantly from the permanent feed for the pump over run? The vaillant wiring diagram shows terminals 4 and 3 on the boiler as linked or remove the link for external controls, but how do you incorporate this into the y plan? I can't work it out any help greatly appreciated.