Thanks techn_nz, I had already confirmed the cables good, had swapped out the fuses and distribution board with no luck.

spent some time to trace wiring and found issue to be a bad chain slack switch on the power side. no error on slack chain though.
all previous checks had been on switch side, no thought given to power side because common to other options working.

Problem now solved.

You need to follow the wire back from the lower solenoid valve and find where the voltage drops from 24 to 2.5, most likely either a mast cable or distribution board issue, swap the fuses first though as that's the easiest fix and i've had corrosion between fuse & fuse holder before that gave the same symptoms.