So its a balmy -11 degrees here south of Cleveland. I have a 3700 sq ft home. In the late 80s the oil boiler was replaced with an electric boiler. This is basically a giant version of an instant on tankless water heater. I have copper baseboard radiators. The last few days I noticed that the house was struggling to maintain the requested heat (When temperatures were still around normal) I then closed one of the 4 zones on a part of the house that is seldom used. A few hours later the house got up to 70 degrees. Today, the house temperature continues to drop. The Taco 111 series pump is running continuously, and the 5 coils in the boiler continue to kick on and off, but the radiators are barely warm. The piping exiting the boiler is hot to the touch. My suspicions are that the fins in the pump impeller are worn off or broken off and the water is not circulating correctly. I have not been able to hear water trickle inside the radiators that I would occasionally hear. The pump is silently cruising along with virtually no humming. Am I correct on my assumption?