Old 1955 boiler 3 zone with 3 pumps 1/2 copper in basement floor radiant and the same in attic

karter

Basment is 1 zone. Works good. 2nd zone. front part of home radiant 1/2 copper in attic over plaster i think could be drywall? Covered with vamiculike i thnk.and 3/4 plywood floor. 11/4 steel pipe drops and runs in basement in joists. 3 zone. Rear bedrooms same setup as zone 2. The prob is. When checking temps on 11/4 steel out and in pipes the pipe from boiler is very hot but the return is not very warm. All other returns are hot. OK I drained system installed antifreeze with a pump. Pumped it i to boiler drain and opened each zone bleeder above pumps to a bucket keeping below the coolant to get air out. Could I still have air in that back zone 3. When we did last time had to keep turning pump off pressure was going to high. I bought a smaller 1/12. Hp pump .was thinking fill 5 gal bucket with coolant pump into boiler drain.then put short hose from return from zone 3 bleeder and put it in bucket keeping it below coolant. And just let it run to see if I can force more coolant in. What should the pressure be on a cold boiler. If it helps may do all 3 zones