Each bedroom has two vents, only ONE vent from each bedroom comes out hot air. There is no valve control at the main pipe.

Must be an obstruction -- or no connection. A fiber-optic camera through the line would help diagnose the problem.

1 is probably a return

Must be an obstruction -- or no connection. A fiber-optic camera through the line would help diagnose the problem.

When you say "no connection", where and what is the connection

Are they in the floor, or the celing?

1 is probally a return

Definitely not a return. It worked before and now the room has not enough heat

are they in the floor, or the celing?

Ceiling