No heat in hot water radiators

Help! Our radiators were diconnected this summer when we bought the house - they worked well before. They were consequently flushed cleaned, painted, & reconnected, and do not work in 3 rooms. I have checked all lines, nothing is frozen, water is in the radiators, I have bled & rebled them all with the key, can feel heat in pipes right up to floor connections, then no heat upstairs from that point to the radiator itself. Basically, there is minimal warmth in one, and none in 2 others. Any suggestions are appreciated in snowy New England!