Hot water baseboard heat: First floor is one zone, second floor another each with t-stats and circulator pumps off a common boiler. I keep second floor ~50F as nobody normally sleeps up there. It appears that second floor was picking up enough heat from the first that t-stat never called for heat, but with it being so cold here in Detroit right now (and water not circulating) the pipes froze up in some areas where they cut thru attick spaces. (I am certain at least one attick space fell below freezing.)
I've been blasting all my attick spaces with electric heaters all day; they are all ~50F. Everywhere I can get my hands on the copper pipes, they are clearly not frozen anymore, BUT I still can't circulate water thru second floor zone.
Circulator pump is getting voltage, humming, and getting hot (just like one serving first floor.)
Ideas? Still a chunk of ice somewhere? Could I have somehow created a big air bubble on second floor? Should I try purging second floor zone with tap water pressure?
Second floor zone was fully functional a week ago when I turned it up for overnight guests, but last several days in Detroit have been very cold.