That's done it!
My situation is not resolved yet though.
Can one attacth a vent to the expension cistern & the feed from the expansion cistern to a vertically climbing 28mm HF from the boiler [before the Grundfos Domestic Circulator-Pump]? in that order? Will that stop over flowing with pump speed at 2 & 3? [My pump is set at 1 at present]
My situation as in the photo?
Regards