This is my 1st post here, hope I don't look like an idiot. Last week here in NE we had biblical flooding. Basement flooded, oil furnace cut out. I reset the burner, and its been fine, but I have one radiator in the bedroom on the 2nd floor that won't get past luke warm. All other radiators on the 2nd floor are hot. I bled the rad, it ws full of water...so I tried this...I turned off the valve at the bottom and bled about 5 gallons. Then I blasted the heat and turned the valve back on, and bled it again. It got a little warmer, but not much.
On my hot water radiators, sometimes air gets trapped in the top part of the radiator. There's a very small valve on near the top of the radiator that opens with a small key (available at a hardware store) that allows the air to bleed out. Not quite sure if that's what you already did from your description.
Also, make sure the fill valve for the system near the boiler is open. Otherwise the system will be low on water now that you removed 5 gal. I know, it sounds dumb to mention it, but two plumbers have left mine closed after fixing other problems.
Many systems have a steel tank with a bladder in it that keeps the system slightly pressurized. If yours has such a tank (mine does) you might try checking the pressure. If it is not the "right" pressure (mine has the pressure indicated on the side of the tank) you need to pump it up with air.
Finally, if the system has a water circulating pump, as mine does, make sure it is working.
I have one room with two radiators, and for years I have kept one turned off. This winter it got so cold in the room I opened the valve on the other one. It took quite a while for this radiator to warm up at all, but after a day or so it finally did. Once it got hot, it worked fine from then on, cooling down at night, heating up the next day, in response to the thermostat. Not sure why it didn't work right away -- perhaps a clogged valve that opened up, perhaps the pressure issue mentioned above (the pressure in the system was low).
That's all I know. Just a homeowner, not a plumber or HVAC guy.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.