I have a gas furnace with baseboard heat. The heat in the basement and on the main floor is fine. There is no heat on the second floor. I replaced the thermostat, and the circulator pump. Still no luck. I drained the line when replacing the pump and then realized there is no water in the line at all now. I started everything up after the replacement and the pump turns on but there is no water in the pipes to pump. I opened the spigot after running it and no water comes out, and the pipe stays cold. The furnace is fine, the pump works, the thermostat works why would there be water getting to the other 2 zones but not this one. Even before I replaced everything I tried bleeding the air out of the pipes on the 2nd floor by pushing in the the 2 bleeders that are up there. No air or water came out.

What pressure are you showing on your gauge?

yeah, it is a common problem with iron body fill valves. they clog with rust and must be replaced.
if you want to change it yourself, post a picture and help is on the way. be aware that the newer style valves are pretty easy to change but the older ones can be difficult.
P/S, just look for the cold water feed going to the boiler. i will have the fill valve on it..

You do not have enough pressure to lift the water to the upper floors.