HVAC in Hartford is old heat in older buildings. Steam radiators in three-families knock and leave the top floor cold when a vent fails. Hot water shows up in later houses at the edges of the city. One boiler in the cellar may serve more than one household. Window units in brick rows drip onto entries all summer because the valley air is humid even when the night is only warm. Start with the machine you have.
No heat on the third floor and a roaring first floor is often air in the system or a dead radiator vent, not a dead boiler. A fuel smell or soot on the jacket is a different call. Tanks in basements sit next to rooms that were finished later. Chimneys built for an older appliance may be the wrong flue for what is tied to them now. A CO alarm that chirps is a reason to stop experimenting.
Outdoor units for ductless heads end up in side yards already full of meters and a bulkhead. They do not cure a steam system full of air. A head in a finished attic does not fix ice at the eave. Summer moisture in a West End brick house loads the air inside even when you would not call the day hot. Radiator valves leak onto floors and get reported as roof leaks by the people below. Say whether the wet ceiling is under a bath or under a radiator.
If the boiler also makes the hot water, a failed coil is both a heat problem and a plumbing problem. Say what you see in the cellar if you can do it safely. You do not need the model plate. You need the fuel, the type of pipes, and which floor is cold or wet. A system that short-cycles all night is not the same as a system that will not start.
Have the neighborhood, the building type, and the symptom. Mention a recent delivery, a burned smell, or a tank you do not trust. Say whether several floors share the boiler. That fact changes the urgency for everyone in the building. Call the number on this page.