So, even though my HVAC guy scraped the slag off of the inside of my boiler, the flue gases still don't seem to be escaping adequately. Or, at least, my smoke alarms keep going off at random times. So now they're coming back to see if there's some sort of delayed ignition on the system. Frustrating.
I also had them look at one of the radiators that is leaking -- I was hoping that a bit of plumbers' putty would solve the problem. No luck -- they're suggesting a new 1 1/4-inch radiator valve. (Plus 1+ hours of labor to swap the valves out.)
The pleasures of getting your heating system ready for the winter....