I purchased a home a year ago and I noticed late last winter/spring that 3 of my 5 rads were not producing any heat. Today I tried bleeding them. The two that work let out a little air and drops of water. The other three that are not working let out a little air and no drops of water.
I suspected that the water pressure is low. We live in a one floor bungalow with the boiler system in the basement. I checked and the PSI is showing around 10. I read that 10-15 psi is what you need, so I'm not even sure if pressure is the problem. The other issue I have is I'm not sure what water valve I turn on to add pressure. I've attached a couple images of my system, and would appreciate any advice and help people have to offer!
10psi would be enough to run a 1-story house with the boiler in the basement. You may have other issues to address other than system pressure.
But to add water, follow the copper plumbing back from the boiler to where the auto-fill valve, which appears to be over your hot water heater. It looks like you may have a gate-valve in series with the auto-filler near the Tee under the floor joists where it branches off to the cold side of the water heater. If it isn't already, open that valve, and if the system pressure is below the preset on the auto-filler you should hear water flowing. If it's already open, there's probably a cam-lever on the auto fill to over-ride the setting and let more water in (the photo isn't clear enough to say for sure exactly which filler valve style that is.)
Be sure not to over-pressurize the system, or you'll have a steaming mess on the floor when the pressure valve on the boiler opens up during it's next burn cycle. I don't see the expansion tank for the system in the picture, but it needs to be properly air-charged for the system pressure too.