This is Nancylouise's husband from the other post. Now I think I
understand your problem. There should be an expansion tank on the
system. Newer systems have a tank with an air bladder, which keeps the water
pressure in the radiator system fairly constant. Otherwise, heating up
the water expands it and pressure would rise quickly. In your picture of the top of the boiler, the auto makeup valve is the one that has the conical top and the blue metal tag on it. There is usually an isolation valve somewhere before it or after it. When the radiators were removed, the isolation valve had to be shut or the auto makeup valve would have kept supplying water to the radiator system and the system would have never depressurized so that the radiators could be removed. Check that any valves in line with the auto makeup valve are open. That will provide supply water to fill the radiators when you open the radiator bleeder valves. Hope this helps.

The description above is correct, and you need to make sure the water supply valve/makeup is on. Then as you bleed the radiators it will allow fill water to displace the air. However, do not bleed them when the boiler and pump are running, just let water pressure fill the system.

It smells bad when you bleed the radiators because the pipes are full of stale, dead water. Its a closed system and if its working right there is no oxygen in the pipes, and the water (and air) smells funky. That smell should only be there while you are bleeding them, and should go away very quickly.

Bruce

Also, if the radiators were painted, ours offgassed when the heat was on for quite awhile - maybe 2 or 3 heating seasons?