Picture a lake house that started life as a summer cabin, gained a bedroom wing in the 1950s, and got a steam boiler somewhere along the way. The owner says the living room heats fine but the addition never warms up. Gary has seen this pattern often enough that his first guess is air, not the boiler. Air trapped in the pipes blocks steam from reaching the far end.
We start at the boiler anyway. Water line steady, pressure under 2 psi, burner flame clean and blue. Then we trace the main that feeds the addition. In these patched together systems the main often got extended without anyone moving the main vent to the new end, or the vent is missing entirely and a plug sits in the tapping where it used to be.
Next we check the radiators in the cold wing. On one pipe steam each radiator needs its own working vent and has to pitch slightly back toward the supply valve so condensate drains out. We set a level on each one, test every vent, and open each valve all the way, since a half open valve on one pipe steam lets water and steam fight in the same pipe.
The fix is usually modest: a Gorton style main vent where the extended main now ends, a few new radiator vents, and some shims under a radiator or two. On the next cycle the far rooms heat up within minutes of the near ones. We write down what we changed and leave the notes taped by the boiler for whoever services it next.