I have an old Weil McClain boiler. It's gas fired but I believe that it's a conversion unit on an oil burner. It has four zones. One of the four zones that heats the upper floor is not heating up. It seems like there might be air in the line as it's warm near the boiler but it cools off a few feet away from the boiler. I can't however understand how to get to the bottom of it and would certainly appreciate some input.
I have attached a photo. The circulator nearest the camera is the problem. The black valve has a hose bib type connection on it. When the thermostat is off, water flows from here. When the thermostat is on it doesn't flow, just light air. I can't seem to locate any other valves on the line upstairs to allow air out.
A few more notes. The other zones work fine. The pressure gauge reads zero. The valve for the incoming line off the water main was closed. I opened it today (it's still open) thinking that it would add pressure to the system it didn't seem to have any affect. The thermostat seems to work fine, it clicks on the circulator when switched on. While trying things I opened the valve on the overflow/expansion tank and allowed water to drain for maybe 10 seconds, no idea if this was a bad thing to do.
Does this sound like air, or maybe something wrong with the circulator??
Any thoughts are very much appreciated.