#8 is the air vent. #5 does look like a pressure reducing valve. I think you have it right.

You will be using water from your pressure reducing valve to fill the line. It appears you'll have to go through valve 4 to get to valve 1 with your fill water. Are you planning to let the water from the boiler fill through line 9 and return to point #1? If so, leave valve 1 closed until the line is bled out. At the top of the red flow valve in line 9, open CCW all the way, the top triangular device like a spigot and close it when you're done. If the circulator starts up and is able to push enough water through the loop, the air will be bled out at the air vent.

I would isolate any other zones, if you can, until you get the basement zone working.

Remember, you are dealing with hot water. Turn off your boiler far enough ahead of time and let all the water cool off in all the zones and the boiler.

Okay, finally I have success! I'll detail what I did as it might save someone a lot of headache.

First off, hot water pipes are thinner than cold water. I think cold water is type M and hot is type L or vice versa. No matter how many times I look that up, I still forget! Anyway, I got pretty good at cutting the thick one but was having MAJOR difficulty cutting the thin one. To make a long story short, I had to use a hand held key saw. Annoying, slow but that worked.

Next, stick bread in the lines on both sides to block the water. You think you get all of the water out of the line, but you don't. With water in the line, soldering will be impossible. You'll have to heat the joints three times as long and the solders won't be good. I had leaks by not following this. A step which I knew but still didn't do. Stupid on my part.

Okay, no more leaks. Now, I'm supposed to bleed the lines. Although my house was built in the 1930s, we added a large addition and the house is pretty new, including the heating system. It seems that the plumbers are no longer putting bleeders on the line. Mine don't have any. No problem. I should just open up point 1 in pic 2, and the valve on point 9, pic 1 (which you can't see) then open the garden house valve on line 1, pic 2. When the water flows out smoothly with no sputtering, the air is out, right? Well yes, but things just weren't working that way. I did everything I just said and water came out. Within 10 seconds, however, all the water came out and it just dried up! Uh, is that supposed to happen? Confused, I shut the line and waited about 30 minutes while I did other things. I came back and tried again. Same results!!! I had about enough of this plumbing project. Looks like it won and I lost. After about 10 successful projects, I was going to have to call in a plumber. I tried getting the job taken care of with my normal service contract, convinced that it was just a lack of knowledge on my part. I was told that since it was the weekend and they weren't sure the project fell under my normal service agreement, they might have to bill me...at the more expensive weekend rate...of $165 per hour!!! I quickly told the lady I'd figure it out myself.

Searching this site, I found the answer. I did everything right except one thing. You have to continually add water to the line so that it keeps flushing the air out. You do that by flipping the little handle on point 5, pic 2. That automatically ensures that the pressure in the baseboards remains at the setting on the reducer by adding water when need be. However, if you open it manually, it will just let the water flow (also pushing the air out with it). If there's air in the line, the pipes aren't going to get hot, so you've gotta get the air out.

With each bucket of water I let flow through, more of the line got hot. Three buckets of water later, the water was flowing smoothly and I had heat! Note that by me doing what I did, I introduced air into another zone, so I had to repeat the process for that zone as well. No biggie. Three more buckets later, that zone was working again! Now I don't know if there's a way to work on one zone while not affecting the others. I'll have to examine what I did a little and see if there's a sensible way of doing it. Anyway, hopefully this helps someone.

nice system! and well done, is there by any chance a drain valve on the main cold return line at the bottom of the boiler? neither of your pictures shows one. also, your system should not require manual flushing of air. the individual loops should push the air to the boiler itself, and bleed out the air bleeder on the top of the boiler. if it's not bleeding air, it may be stuck or clogged with gook. next time, just remove the schrader valve from the bleeder (#8 in the first pic) if nothing comes out, it's bad, replace it.

You could have hooked a garden hose to the end of the loop and placed the end of the hose higher than the highest radiator in the house, outside, until the air was out.

Please invest $20 in a copper tubing cutter for your next project :)

"Please invest $20 in a copper tubing cutter for your next project :)"

- ...and 2 loaves of bread.

Good job.