That's good news Ken, I would set it to CC3 to start with, if you have to close all the rad valves individually (no u/staors/d/stairs zoning), then just run it as is, ie, if d/stairs only opened up now just start the pump and post the numbers, you can then open up the u/stairs and run both systems together on CC3 and have a look at those numbers.
Don't know what the total rad(s) output is but assuming 20kw max then the flowrate required will be 20LPM (1.2M3/hr) at a rad dT of 14/15C/kw which would result in a pump head of 4.7M in CC3 mode, see what you come up with anyway and you can decide on balancing, if any, is required later.
My system, 12 rads, 20kw, no balancing, works fine at a 3.5M head.