Airbound hydronic system

NHLadyWithDogs

Hi. It's a long post, but I want to provide as much detail as possible to hopefully get an accurate diagnosis/ fix. I think I have the right idea, but the steps I took may have been out of order.

I'm fairly certain the main issue is that the system is airbound. There may be other issues as well. Below are photos that I hope are helpful. If you need me to take a photo of anything else, please describe it and I'll do it. I have a Weil-McLain boiler and Beckett AFG series burner. I live in NH. My home is one level, built in 1938, 1,000 sq. ft., with two zones, with Honeywell zone valves. I replaced one zone valve in 2014 with the help of a do-it-yourself forum that employs experts and it's worked great since (it was stuck open). I've asked for help there for this issue, but I'm not receiving the same level of instruction as I did back then, so I'm finding myself becoming more confused as time passes. There have been tears! haha but I know I can do it. I'll list the symptoms of what's happening currently and what I've done so far.

1. Heard gurgling in Zone 2 a few months ago. This is the current "cold zone". For some reason this didn't register to me as a problem, so I let it go.
   
2. On 3/13/21, I woke up to a cold room. 59 degrees. The temp normally drops because I let the dogs out and leave the door ajar so they can push it back open. On this day, I closed the door and bumped the thermostat from 67 to 70. I heard the system start, but the room didn't get warm. Cold baseboards. Replaced the thermostat battery, just in case.
   
3. I learned about bleeding the system at the baseboards. Air was released and this one baseboard out of 4 became warm. Another had no water. The other two don't have air vents. Oddly enough, these two are in the newer addition to the house. I don't know when it was added.
   
4. I went to the cellar (dirt, uneven "floor", access from bulkhead) and tried to bleed the air from a pipe at a ball valve/spigot. Water came out, the slowed to spurts, then down to nothing at all. I tried the other two, and had the same thing happen. The second photo below shows the pressure gauge at this point - 0 psi.
   
5. No one instructed me to do this - I put very hot water in a plastic bottle, much like a ketchup/ mustard bottle at a casual or older restaurant. I took an air vent off a cold baseboard with no water, and squeezed the hot water into the pipe, holding the bottle flush with the opening. I realized the open pipe would suck in air, so I closed it when refilling the bottle, and continued to add water. I could hear a whoosh of water... kind of, release. The baseboard became warm, as did the two with no air vents.
   
6. The system ran the rest of the day, but overnight, everything reverted to the original condition. I added more hot water, system ran. I did this for several days.
   
7. After watching several videos, reading forums, and consulting many articles on inspectapedia, I decided yesterday that I would try to introduce water through the water fill bypass valve. I followed these instructions: https://inspectapedia.com/heat/Air_Removal_Valve.php
   
8. I turned the boiler power off and returned about 90 minutes later. With the power still off, I attached a hose to the boiler drain. I opened the bypass water fill at about the halfway point, then opened the boiler drain.
   
9. I filled a bucket with boiler water while watching the pressure gauge, which was still at 0. At about 10 psi, I turned off the boiler drain and the bypass - however I don't remember which I did first. I learned this morning the bypass should be shut off first. BUT... see third photo below. I only turned it off here (circled in green), and realized in a minute that I didn't shut the yellow lever.
   
10. I turned the boiler on and watched the pressure, expecting it to go to 12, then stop.
    
11. The pressure climbed to about 18 and two pipes began to leak. I opened the boiler drain again to try to release some pressure. It didn't go down.
    
12. I grabbed a second bucket and went to the pipe that was leaking and had a ball valve, and opened the spigot there. At this point, I realized the bypass yellow lever was still opened. I closed it and turned the boiler off.
    
13. I believe the next step I took was to close the boiler drain. I was focusing mostly on staying calm and getting the pressure down, so I'm not sure if this was the next step.
    
14. I went back to the leaking pipe, continued to drain, and the water slowed to a trickle, then nothing, as it did on day 1.
    
15. The pressure gauge was back to 0 psi.
    
16. I came inside and turned off both thermostats for the night. I used space heaters last night. I needed to be calm and rested before turning things back on. So that's where I'm at today.
    

I was told on the other forum by another member (not an expert) that the air vent on top of the Taco air scoop most likely needs to be replaced. I was given a link to buy one, but I don't know if this is the correct part. I was also given a link for Watts automatic air valves to be installed at the baseboards, replacing the coin valves I have. The size looks completely wrong. I don't know how these are measured, so I have a photo of both components alongside a measuring tape.

Thanks so much if you have read all of this and have some words of wisdom.


Original state of the pressure/temp gauge:

Green circle indicates the bypass water fill switch

HVACNUT

Show pics of the piping  to the emmiters. Baseboard, radiators, convectors, whatever. Is it one continuous run, in and out from one emmiter to the next, or what I'm guessing is, a perimeter loop around the cellar, and branch pipes to each emmiter. That would be a monoflo system and air needs to be bled from the emmiters, with pressure on the system. There are valves built into the circulator flanges but they're probably seized. And I don't see a purge valve above the circulator. 
It can be a long, tiring process to bleed the rads but that's the way it's done. Keep 12 to 15 psi on the system while bleeding. It should maintain pressure automatically through the pressure reducing valve. If it doesn't, then the PRV is faulty. 

STEVEusaPA

You obviously have/need a tech to perform annual maintenance (I hope). Why not have them come over and help/show you?
Even though that boiler may hold up a few more years (at least), there's a lot wrong with the overall piping and it's components. Plus there are leaks everywhere that should get attention.
The best advice would be to re-pipe all the near boiler piping, with proper, modern components, especially air elimination. The air poop is basically useless.
With a re-pipe, the water side of the system will be problem free.
Then, in the future, when it's time for a new boiler, it's a simple change out as all your near boiler piping will be fine.
Of course doing it all at once, modern efficient boiler, proper near boiler piping and modern efficient components is the best option, but it's not in everyone's budget (is it ever?).
Unless you have column radiator, almost all baseboard radiator systems can be purged and bled at the boiler. Keep the pressure up, isolate zones. Just can't see enough of what I need to see to give you an exact method, but like I said, have your boiler/burner tech come over for a visit.