Solaris 30PC?

Hot water is good. Central Heating Flow pipe gets very hot, return is cold to touch. Boiler is mounted in cupboard upstairs, upstairs radiators get hot as does furthest rad downstairs, eventually. Big Rad in lounge not getting hot, no air in radiator. Distribution Pipework is plastic 10mm off manifolds fed by 22mm. Pump is turning when end cap removed but suspect not pumping - is only way to check to take out pump and strip it down ?