Possible circulation pump issue - BB HW heat?

Having what appears to be an issue with the heat, the issue being not enough. house has hot water BB heating with a boiler made/installed during the Nixon administration, and I have no idea what it's make/model is.

House isn't heating up normally, it IS heating though. Stat was set to 72* but the temp was only getting to 68* and staying there. I thought it was just a case of being so cold out ( combined with the terrible 1960's insulation ), that the system just couldn't keep up. Dialed back the stat to 68* and the temps dropped to 66* and stayed there.

Boiler is firing, and the pump motor is running, that I visually verified. The circulation pump is a huge contraption - fairly large impeller housing with a motor the size of one on a table saw attached to it. That's compared to the circ pump on my old house which was smaller than the impeller housing on the one I'm in now, "all-in", motor and all.

I can feel water going through the pipes.......but the baseboard units just aren't putting out much heat??? Is it possible the impeller broke, or stripped off the shaft enough that it still spins, but just not at the velocity/volume it's supposed to?