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Radiator Balance/Boiler short cycling issue
One pipe steam, additive pressuretrol. HELP.
Brief History: System has worked pretty well for years, after some work to balance it. This despite the fact that the Main vents were undersized (after two different plumbers told me nothing else could be done to replace the ancient ones because the thread size was too small for newer ones. I wondered then--I'm smarter now--and ticked.) Thinking back, probably not working as well the past few years--but not enough that we really noticed it.
First, no heat at all on single digit day--despite boiler running non-stop. Had plumber in. Said not getting enough gas--check with PSE&G before he replaces boiler gas valve. PSE&G fixes it--condensation in the outside line had frozen. Said pressure good--probably better than before.
Second, next really cold snap, pretty similar symptoms. Called PSE&G first. Pressure checked out ok. Saw crud underneath and said boiler cracked--but it has not been losing water. Plumber comes for second opinion--no crack at bottom, tests for crack at top--all good. Checks pressure controls--badly clogged pigtail. He replaces it. Things much better, but radiators in stack (1st, 2nd, attic) farthest from boiler not heating.
Third, I do some research--maybe bad main vent. I take it for replacement and explain it's a hack, and I really would rather the right size--they give me Gorton #1 and parts to downsize threads. (Other main was same, I replaced it too with right size--#1.) Those 3 radiators still cold. So I research pressuretrols. Cut in was set at 2.5, inside dial at 2. (Additive) I lower cut-in to 0.5 and dial to 1. Better. Downstairs and most upstairs rooms are lovely. First floor rad gets heat--after an hour or more. 2nd floor takes 3-4. Nothing in the attic. This is in the morning. Boiler seems to be running constantly till it gets up to temp--at least every time I check. Later in day or evening I am less clear on--though attic rad got a teeny bit of heat last night before system went to night temp.
SO: I am thinking I need to get bigger vents on those radiators, but I want to know if I can just change them and leave the rest alone. Also wondering if I should have a #2 on the long main--though it does not have any risers off of it--and as near as I can tell the far radiators must come off a short end riser(s) which then goes over. And/or could something else be involved in the short cycling?
I can do pictures as needed.