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This is a classic row house with a single pipe steam heat system. So there is:
Basement - Utica boiler with a wet return
Garden apartment - a previous owner removed this floor from the steam heat system
Top 3 floors - these have the steam heat.
The boiler cracked over 10 years ago and was replaced with a Utica system that has a modern smaller water capacity. I don't remember issues the first few years. The boiler has a McConnell & Miller PSE-802-24 low water cut-off and a McConnell & Miller Uni-Match automatic water feed. The low water cuts-off on each cycle and if the water feed is allowed to run, progressively more water fills the system. So, I have too much water yet the low water cut-off still cuts-off. I got lazy about checking the water for a couple weeks and found water coming out of a radiator on the 2nd floor.
I had an incident where the boiler appeared to be full of sludge, presumably the gunk from the wet return. The plumber said no problem and drained and refilled the boiler.
To address the short-cycling I had the wet returns replaced. Judging from the sight glass the water returns faster but not fast enough to prevent the short-cycling.
I had a follow-up problem where the water in the sight-glass was not accurate and I inferred there was some gunk blocking the sight glass. The plumber cleaned it out and replaced the sight glass.
With the automatic feed cut-off closed, I need to add water every 3-4 days. If I add enough water to fill the water near its maximum sight glass line, I get water hammer in the pipes near the boiler. You hear it through the house but it's definitely happening in the basement.
I had the vents on the risers in the basement replaced and replaced all radiator vents and ensured the radiators are tilted to the return. I have a radiator that sometimes sounds like water is boiling but there is no water hammer which I find odd. Another radiator that has a tapping sound at the start of the cycle, the taps speed up and simultaneously fade out.
Appreciate any help on this, thanks.