Two stage gas valve

@Fred, Yes that is what I meant, I listed 3.4 per section just in case I counted incorrectly.

@gfrbrookline , I too noticed how clean it was under there!

The potential output of that Rad is about 15K BTU. I'd like to see how it does after the vent is properly positioned. It may be enough. If the room is still cold, a heat loss may need to be done on that room. I kinda suspect it may be enough . The cathedral ceiling and if the side walls and ceiling are insulated is the big question.

@gfrbrookline I recommend against insulating anything, the boiler is waaaaay oversized and they need to almost waste heat. Steam getting to any radiator with that boiler won’t be a problem, it’s a matter of balancing.

It is much easier and cost effective to move the vent.

Also make sure to swap out that varivent with something much slower. The varivent will vent way to fast and add to your problems. Again I would recommend a Ventrite No. 1 so it can be dialed in.

gfrbrookline said:

@Dave0176 now that she has the 2 stage gas valve most of the oversized factor will be diminished. I am also oversized by about 50% purposely by my previous contractor because my boiler also heats 2 80 gal indirect DHW tanks and a hot water loop for the basement. My mains and returns are now insulated and we were able to overcome short cycling by massing out the main venting with a total of 7 big mouths and 3 G2's and choking the radiator venting way down. The heat is also now even throughout the system, granted much larger system than the one in question. Granted every system is different.

If I knew then what I know now I would have found a different contractor who better understood steam and found a different solution for the DHW.

When the boiler finally goes into low fire at 14 oz, they get about a 2-3 oz drop in pressure, then the pressure begins to rise once again, at about the 5 min mark since low fire kicked in pressure has risen to about 1.5 lbs, within another 10 mins the pressuretrol kicks the boiler off at 2.5 psi all in low fire, it will remain off until pressure goes down to about 3-4 psi and will restart in low fire, because the vaporstat high fire cutin is set lower. I tried to calibrate the pressuretrol but couldn’t get it to cutout below 2.5 psi and come back on again. I told them the pressuretrol is faulty and needs to be replaced, Honeywell’s QC is absolutely terrible. Even on the vaporstat the scale means nothing as I have to use my low pressure test rig to set these things up to get the cutout cutin where I want them and I couldn’t get it below 14 oz pressure. Unbelievable terrible QC for an expensive item.

@Dave0176 @cynthia07104 I saw in the beginning of the thread that @Dave0176 recommended replacing the main vents with big mouths, I don't recall if this happened. That will help with the short cycling, you may benefit from more than one on each of the mains. Vent them faster and you can reduce your total run time. But get a properly working vaporstat first.

I think part of your pressure issue my be related to radiator venting. I know you found two radiators that had the vents on the wrong side. What are you venting your radiators with? With sunrads I would use only Gorton #4's, Hoffman 40's or Ventrite No. 1's, maybe a Gorton #5 on a particularly large unit. Anything larger than that is going to cause the radiator to shut down before it is heated through and make the boiler build pressure prematurely. It look me a long time of trial and error with vents, and convincing my fellow condo owners that slowing down all of the radiators in the system would actually give us more even heat and lower our heating bill. All of the contractors we had in over 20 years just kept telling us to put faster vents on the cool units so at one point we had 10 Gorton D's, 10 Gorton C's, 5 Gorton 6's and 6 Gorton 5's, we were totally out of balance and the boiler cycled constantly. That's when I found this site and ordered Dan's books. Now the largest vent I have is one Gorton 6 on a 10 section 3 column radiator with an edr of 80 that is farthest from the boiler, most are Gorton 4's, Hoffman 40's and Ventrite No.1's in units that I know the owners won't mess with them. It made a huge difference in balance and eliminated the cycling.

You are in good hands with @Dave0176, I have read many of his posts and have learned much from them.

Sounds like you are on the right track!