Convector not getting hot (possible reasons?)

mcops

I am trying to understand why my convector is not getting hot. It is a single pipe, monoflow system with an old boiler. It is going to a second story unit. There are (8) convectors. It seems that convectors (2,3,4) in order from closest to the hot boiler supply have the issue described below:

1) I feel no heat coming from the convector
2) The supply line feels hot at the top near convector, the return line feels too cool.
3) I bleed out for a couple minutes, over 1 gallon of water. It seems any air would be removed. While bleed the water starts warm then gets very hot. I notice the return line (both near the main and top where I can touch) gets very hot, indicating the flow is coming up through the return.
4) the monoflows are definitely piped in the correct direction. There is also plenty of length between the Tees.

Based on this, I am trying to understand what is happening from an engineering perspective. In particular:
a) should I be surprised by 3)? I expected the flow to come through the supply while bleeding
b) it seems I am getting no flow, not enough pressure to push through this convector. this could be due to
- an air pocket in the supply line to the convector which cannot bleed
- a faulty/corroded monoflow T

Is there anything else that could be the reason? Is there anything else I can test/try? Thanks in advance for any comments

EBEBRATT-Ed

Monoflows are difficult to get the air out and with long runs to the second floor even more so. Try raising the pressure in the system to 20-25psi and try bleeding again. If you get them working, then lower the pressure by draining at the boiler. You may try bleeding with the circulator off and then with it on.


If that doesn't work the sure fix is to drain it down and put some valves in the branch piping, then you can open the valve one at a time so you can bleed each pipe.