Upstairs radiators are barely working
I am hoping that some fellow old house owners here have radiator experience and may be able to help me out. The problem is that my upstairs radiators are barely working. When I bled my radiators last week, the upstairs radiators only bled air and not water. Thinking I perhaps didn't get all the trapped air out the first time, I tried to bleed them again yesterday and got more air and a little water out of all but the last radiator I tried to bleed.
The downstairs radiators are working just fine, and the pressure gauge on our boiler indicates it's at the optimum PSI (according to the info label on said boiler.) When we crank the thermostat up above 70, the upstairs radiators do get warm, though they're not as hot as the downstairs radiators.
I am guessing this might be a pump problem, since the downstairs radiators are full of water and the upstairs ones evidently are not. Does anyone have any ideas or insight on this problem before I call an expert in?