..Pic of the pump wall
From the piping of the secondary pumps, it appears your primary loop is pumping TO the remote boiler-- Is that correct, or have I misinterpreted your piping?
Where is your expansion tank? Good hydronic practice locates the primary pump after the expansion tank, so that your are pumping AWAY from the boiler, and TO the secondary loops.
If for other reasons you want to keep the primary pump at the 'pump wall', you can fulfill that requirement by relocating the pump ahead of the first set of secondary 'supply/return close tees' -- i.e., [the pex supply FROM the boiler] >
[primary pump] >
[the upper copper pipe] >
[tees to Grundfos pump] >