Yup, the circulating pump which supplies seawater for the heat pump (to chill, thus providing the heat...) was, well, *not* circulating. The pump motor was warm, indicating that it was getting power, but apparently the impeller was not turning. I tried flushing the system backwards by directing a stream of water from a hose into the discharge thru hull, but no joy. And finally, no amount of percussive maintenance (I stopped just short of destructive percussive maintenance) would get it to move water again.
So I dug out the old space heaters (yes, we still have them on board, thankfully!) and plugged them in. I also lit the Dickenson diesel heater. So now Eolian is back to being heated the same way she was before the heat pump installation. And it is cold outside here in Seattle - but never fear, we are cozy here down below.
I called the heat pump manufacturer in Florida, and he promised to have a new pump here in a couple of days.