We lost heat in 2 out 3 zones again yesterday. Slept in the basement where the heat still worked. Plumber is here now replacing the circulators. The entire system was just drained and a small amount of crud came out of the water, which could have locked up the circulators I guess. Didn't seem like that much to me, and I was here when the new furnace went in and watched them flush the system beforehand. Plumber says that particular circulator is just a crapshoot.
I know nothing about these things, but just looking at the new circulators going in now they appear to be 3x beefier. That has to be a good thing. I think?