Loud hissing from nearly all radiators during this cold spell

I do that. My contact info is below

Not sure if these issues are related.

Yes, they are related

from here, I would first verify the pressure regulation was working

Then if vents are leaking under normal conditions, they have to be replaced

I don't know why the link is no good. Trying again:

https://www.youtube.com/%40gordonschweizer5154

https://www.youtube.com/@gordonschweizer5154 /search?query=pressuretrol

Go to youtube. search on Silent Steam Team. Go to "videos". Search on "pressuretrol". That should get you to the ones for your pressuretrol.

We need more pictures. Front, and other side of the boiler, showing all the piping going out of and into the boiler.

Better picture of the pressuretrol, closer up and in focus, with and without the cover (only one screw to remove cover)

Can't tell what I'm looking at with your boiler piping photos. Need pictures a bit further away and from multiple angles. But, it looks like your header goes into a bullhead tee with one side going up to the main and the other becoming the equalizer. That would be super wrong.

We need photos of the other side of the boiler showing the Hartford Loop. Measure with a liquid level (clear tube with water in it and a helper) or something, from the top of the Hartford Loop close nipple or elbow to the normal water line of the boiler (should be marked by manufacturer)

We still need that crucial photo of your pressuretrol with the cover off (remove one screw at the front bottom), showing the internal dial setting. It looks like your cut-in may not be as low as it could go.

That radiator valve is not working in the off position probably just old.

bob

Did you watch the video? If money is not an object sure but plumbers are crazy expensive. It is a pretty easy repair. It is really a handyman friendly job so you wouldn't have to hire a plumber and pay the trip charge and all that.

Probably better off opening it back up because it may be acting as a one way valve, letting steam in but not letting condensate back out, except for the vent. On second thought, if you want to keep it turned off for now though, I'd remove that vent and put a plug (pretty sure it is 1/8 in. NPT) in it's place and keep the valve closed until you can replace that valve.

Yes any supply valves that are hissing or leaking are bad and need to be repacked or replaced. Any vents that continually hiss after steam has already reached them are also bad and need to be replaced. If steam has not reached the radiator vent yet and it hisses it is just releasing air from the radiator as steam advances and the hissing in this case would be normal if the pressure is much more than a couple tenths of a psi.

I don't know what your overall connected sqft of radiation is relative to your 746sqft of boiler rated steam capacity but if your boiler is at all oversized you have to make adjustments for extreme cold weather. I have a 35% oversized boiler yet most of the winter am able to do 5 or 6 degree setbacks and recoveries without issue because I manage those recoveries broken up into controlled on off cycles that limit continuous firing time of the boiler thus avoiding pressure rise. Pressure only rises in the system as radiators one by one start to completely fill up since then there is less place for the steam to go and the boiler doing what boilers do continues to make the same amount of steam until either the thermostat, the pressuretrol or the low water cutoff tells it to stop. So, to avoid all this in extreme cold weather think about what you can do to avoid all or most of your radiators completely filling and thus building pressure. Answer:

1. Minimize the required heat - Lower or eliminate your setback if weather is going to be extremely cold. Only you can define what extreme cold is for your system based upon your experience. I am one of the few proponents of setback on this forum but where they do save me money on normal winter days, once night time temperatures get below 15 degrees or so they don't do anything for me but make morning recoveries noisy. If your system only needs to raise the home temperature a degree it is going to take less cycle time than 2, 3 or 4 degrees. I normally go from 59f to 66f but last night and the night before here in Michigan I just set the temp on hold a 65f and went to bed… (-14F this morning)
2. Run more shorter cycles - Setting your pressuretrol or vaporstat lower will do this to some extent but they are both still reacting to some level of pressure rise which indicates you are already running a longer cycle than optimal. One simple thing most people can do depending upon your thermostat is to adjust your thermostat control to help minimize cycle time. If a cycle per hour type setting then set it for the cold snap on 2 instead of 1. If a swing temperature range type control set it on +/- 0.5 degrees instead of +/- 1 degree. You can always switch it back if you care to after the polar vortex has passed.

When it comes to the main venting it looks like you have a Gorton #2 on each main which may be sufficient. Have to know your total steam main lengths and pipe sizes to know for sure. Where more main venting makes the most difference on a system is during extreme cold snaps because most of the heating cycles start off with very warm steam main piping and thus the rate of steam advance is less hindered by condensation in the mains themselves from heating up the mains. This isn't going to change your late cycle hissing though, only any hissing that may occur early in the cycle after the boiler starts creating steam and before the main vents closed.

Yeh, my 0-30 gage doesn't move even when when my true pressure reaches 1.5psi. I verified this when I was tweaking the settings of my pressuretrol.

That single Gorton #1 is way undersized for all that piping that it has to vent (mains plus dry return). You could do a tree and add a second one or you could just put a Gorton #2 in, which is about equal to 3 #1 and only slightly more expensive. Also, I'd insulate the long nipple you have going up to that vent.

I don't like that type of main where it tees off in two directions but that would be super expensive to change so you are probably stuck with it. So hard to balance, especially with only one shared vent location after the dry returns tee back together. Would be much better to have separate main vents at the ends of each subsection after the tee in the main.

What is the height of the top of the close nipple in your Hartford Loop relative to the normal water line in the boiler. That one photo showing the level in your sight glass looks like it could be below the Hartford Loop. That will cause water hammer and prevent proper return of condensate to the boiler. My opinion is too many clown installers are putting the Hartford Loop way too high.

My pressuretrol originally with the same settings you are at (0.5 main, 1 diff) let my pressure rise to just over 3psi. I was able to tweak it to shutoff at 1.5psi but you would need the new gage to attempt this adjustment. Some pressuetrols simply may not adjust down far enough before not letting the the boiler cut back in.

I've never used this stuff but I bookmarked it a while ago:

Iron Paste

 withstands temperatures up to 400° F and also withstands pressure up to 60 lbs. on water, oil, steam or gas lines.

https://www.blackswanmfg.com/Category-04/Iron-Paste.HTML

I just had the same issue. Turns out my pigtail was clogged. I took it off and cleaned it and my system immediately went to near silence. Try removing and cleaning out the pigtail. It took me about 30 minutes to do.