Both replies were very helpful. When I opened the hex COLD water shot out right away... no air in the line, but no heat either. I chipped away the paint on the inlet valve and opened it with a vice grip. The only strange thing is that I assumed "opening" the valve meant turning it to the left (counter-clockwise) like an outdoor spigot... Turning the valve clockwise opened it and I heard water begin to flow instantly. Thanks to you all I now have heat in my bathroom! ;-)

One problem that a lot of heating guys make when replacing a pump in a old system likes yours where there was steam radiators that have been converted to water. Check the size of the pump, If he took a hi velocity pump off and put a standard pump on, it will not flow enough water to heat right. I don't know what your piping system is and how many story house you are talking about. You might have a mono flow system and they take a HV pump to flow more water. Later Paulbm

You stated that this is a new installation with your rehab. Call your installer and explain that you have not previously had to use the heat, but now that you have tried it, you find that radiator is not working. As was mentioned above, it is probably just something simple like bleeding air from the system or adjusting the water level and your installers are fully aware of that, BUT- At this time it is not a DIY project because any changes you make to the system could void your warranty.

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.