Radiator hot on the bottom but not on the top...?

Question

I have a hot water radiator system in my house. The boiler fills automatically from the water line so I do not need to manually add water. I was bleeding the radiators last night and the entire first floor, the radiators bled fine. I went upstairs and two of the radiators are partially hot and the top half is cold. When I bled them air came out for a few seconds and then nothing no air or water. The third radiator was completely cold, so I closed the inlet valve and reopened it. It then began to get warm and bled air and then water. However, I tried to bleed the two that did not produce water again and the same thing happened. I heard air for a few seconds and then nothing. Is there something else I need to do? Or should I continue bleeding them for a few days until water comes out?

I didn't see a pressure gauge on the boiler. The only gauge is the temperature.

I thought it may be filling slowly, but the one that was completely empty filled in a matter of seconds and it is on the same floor.

Last night I noticed something strange. If I bleed the radiators that are not filling all the way when the heat is off, they suck air in, rather than push air out. If I do it while the heat is on, they push air out for a little bit and then nothing.

Answer 1

Have you checked to see if the water pressure is what it should be? Could be low enough that gravity is halting progress.

Answer 2

Just Keep Bleeding Them. It's Filling Slowly

Answer 3

Sounds like there might be something partially blocking flow to the problem units. Try bleeding them a couple more times, it might break loose.

Answer 4

I think you have an air lock somewhere, put that into google, and see how you can fix it. Good luck!