Basement radiators cold, suspect air lock

Just remodeled a basement bathroom (used professional plumber!). We had disconnected a cast iron radiator in order to put in a new floor, walls, etc. Now it's back in but not getting hot. There is another radiator in this zone, also no longer heating. The other two zones in the house are fine. We drained the entire system, bled all radiators, still no heat. We also put a hose on the basement drain, closed all the other zone valves, and opened up the intake valve, raising the pressure to 30 PSI. This had no effect, nothing came out the drain. Pipes stay cold on the down stream side of the valve.
Pipes run up, over and down to each radiator. There are no air release valves on the upper horizontal runs, so no way to get that trapped air out. I assume that's the problem.

First question is, do I need to install air release fittings on all of the horizontal runs? My basement zone goes up over down up over down up over down - three sections of horizontal pipe higher than my radiators.

Second question, what's the most cost effective fitting to use here? I'm on a waiting list for my HVAC contractor. It's practically winter here in Minnesota and everyone is calling for maintenance, so I may end up doing this myself.

What type system do you have? (loop one pipe two pipe) If your not sure post a picture of the boiler along with the piping.

Hey there buddy! Heres a bit of advice all the way from Lehighton, Pa.
I'm assuming that you have a Hydronic heating system with separate heat loops since you have heat in some areas and none in others.
First I must warn that almost all of these heating systems should never be operated higher than 12-15lbs psi. Most systems have a feeder valve which you refered to as an intake valve that automatically provides those pressures. Feeding extra water into the system can cause leaks in your heating system.

Typically when I service heating systems, I install ball valves at the return side of each loop so the separate sections of the heating system can be isolated. Before the valve a boiler drain valve can be installed so when water is forced through the system it is forcing all the air out with it. When you have a solid stream of water, close it off and your good to go.
Also check to see if you have multiple thermostat controlled zone valves and be sure they are funtioning.
Hope this helps!

Three zones, three t'stats, ball valves on outbound and return lines,but only the basement has a drain. System normally runs 16 psi but contractor who installed it said to pump it up to about 30 temporarily to try pushing out the air. That didn't work and it's now back to 16.