38.3F and clear @ 06:45 ...
Went back into town for round two yesterday ... blew the boiler system out again, got a little more water out of it. Something's not entirely right and I'm not sure we've got it entirely blown out ... but the compressor is due back this morning. The boilers themselves are empty, that I am sure of.
The system appears to hydro-lock for some reason ... you open a combination of valves that should provide a pathway to daylight (out one or both of the boiler drains) and you get nada ... no water, no water vapor, no air ...
I'm beginning to have a sneaking suspicion that the other, older boiler may not even be functional. Part of that stems from the drain cock on the boiler itself being plugged with sludge and having to be replaced, as well as a section of line coming apart upstairs. And my former tenant's apparent inclination to avoid doing any maintenance whatsoever unless he absolutely had to.
Since the upstairs floor of that building was essentially unoccupied - except for when someone had to run upstairs to get an exhaust pipe - I'm thinking that he may have had one of his employees shut off the upstairs loop at some point to avoid heating it. If so, who knows how long that has been going on.
The other possibility is that the second boiler failed at some point, and he didn't inform me about it, because he didn't want to pay to have it repaired/replaced.
Thinking about the way it is plumbed (two boilers in series), the spider's web of piping makes sense: with two boilers (rather than one) you have some redundancy - if one fails, you still have the other one to fall back on. Might not be all that comfortable, but you can still heat both floors of the building and at least keep it from freezing.
Wife got the front lawn mowed while we were there.