The appearance of the water in the site glass looks fine---I think all that is necessary at this point is to do a quick weekly blowdown as described previously.
What does "the ones on each rad" mean? What is a rad? Where are these air vents located?If any of the air vents (the main ones in the cellar, or the ones on each rad) start to clog up then that would be an indication that the system needs a cleaning.
The homeowner's manual would specify the procedure for this---but this is best done by a contractor, as nasty chemicals are involved & serious eye injury is always a possibility.
It sounds like you have a hot water takeoff on your boiler for the domestic hot water taps---in this case, the system is not producing quite enough hot water for your family's needs---so yes, the water level on the sight glass has to be bumped a little higher.
A plumber who came over to do an estimate for us recommended this, as well. This is a good idea, even though I don't like the thought of heating water that is not being used right away.If your family is constantly running out of hw for showers, etc., one way around this is to install a 30 gallon or 40 gallon INDIRECT HOT WATER HEATER.
Basically, a coil is run thru the 40 gal. tank & the hot boiler water is circulated internally to heat the domestic hot water.
Such units by Triangle Tube Phase 3, HTP superstor, Crown Megastor, TFI Everhot or Amtrol Boilermate are highly recommended.
Typical unit cost is $700-$1k plus $300-$500 for installation---these units are highly recommended---they last for decades without problems & you'll never run out of hot water.[/QUOTE]