No its not a joke .

[townfanjon]

If it is a system boiler with S Plan, just feed new system pump from the SWL, so it runs whenever there is a demand.

Cheers Gotch ya . I did some CCT’s on a Viessmann and they made a separate box to wire it in to “if memory serves “

 

[dan_the_plumber]

Could be an air lock. Rubbish all rads except those not working. Then attach to hose to hopefully a drain off on or near rads. Open filling loop and build up to 2.8 bar pressure. Then open drain off and filing loop simultaneously. Hopefully this will force any air out. It might also dislodge any blockage that may be in that particular leg.