No heat from bedroom 'radiator'
Hello, I live in a condo built in the early 60's, I believe the heat is hot water.
I have 7 "radiators" around the condo, they aren't standard radiators, they are indented into the walls and only contain a small pipe with fins on it. I posted a picture below of the inside of the bathroom radiator, all the others are the same except they are much wider.
Last year at the beginning of the Winter I bled all the air out of all the radiators by simply removing the cap from the tire stem type fitting on the top right hand corner (see picture) and turning the valve below it. I let the air out and closed the valve as soon as water started coming out, this was enought to give me heat all Winter. I keep most of the radiators turned off (valve in lower left hand corner) because I like it cool and I get a lot of heat from the unit underneath me. I usually only turn them on when it's real cold.
Fast forward to this year, I go around and bleed all the air out of the radiators around the beginning of December. They all work except for the bedroom. I go back a week later to try and bleed more air out, yet only water comes out.
A month or so later at the beginning of this week I try again, this time using a tube so I can drain some water out too without it going all over the place. When I open the valve I get a shot glass of water out then a lot of air. As soon as this air is out the radiator works well, it gets my bedroom to 74 degrees while it's 28 degrees outside, WAY too hot for me, so I shut that radiator off.
Two days later it's down to 12 degrees outside and I want some heat in the bedroom, so I turn the radiator on. This time no heat at all, ice cold. I open it up (big pain to get the metal cover off) and try to bleed it again, this time a lot of air came out yet it's still cold, no heat at all. I continue to bleed it but only cold water comes out.
So what could be the problem? I'd think it was something outside of my unit, but I was able to fix it the other day just by bleeding it, yet when I bled it before that it didn't work. It seems like there is still air stuck in it. Any advice?