I have lived in my 140 yr. old home for 16 yrs.
What I have done is:
Just prior to turning the heat on for the season – flush out the boiler by draining it almost all the way, continue to refill and flush until the water coming out is clear, turn on ALL of the radiators at the same time to maximum level (turn valve on), turn on boiler to check that all of the steam air vents are working, then turn down the radiators to heat level desired. This has worked and ALSO eliminated all of the noise that I used to have when I didn’t flush it regularly. Now when the pipes make noise – I know it is because the boiler needs to have more water.
It is important that you have steam air vents on each of the radiators, there are many types depending on the type of radiator you have. I have 4 different kinds of radiators in my house ranging from “baseboard type” to low level “fin type” and also 2 different kinds of the “standard cast iron upright” tubes – (these are my descriptions based on appearance and are not by any way the correct names)
The radiator will not work correctly or at all without steam “air vents” –
The vent needs to be replaced when it starts to make a very load hissing noise (some hissing is normal – but not normal to be really load and have moisture come out) I have 6 different kinds of steam air values on the radiators – some of which help control the heat produced. HOT WATER air valve usually DO NOT work.
Good Luck – you’ll be an expert soon too