RT,
I just replaced a fried CCU that I believe was done in by my frozen (as in siezed) circulation pump. The actual pump can be separated from the motor and taken apart. It's pretty simple so there's not much you can fix. I got mine going again and wired in a 1.5 amp inline fuse. It was a good thing too because I later found the fuse blown and the pump frozen again. After one more futile attempt to fix it I just left it with the blown fuse. I have a hard time spending $100+ for a new one. Granted it doesn't get too cold here but we still use the heater a lot in the mornings and I can't tell the difference. Leaving the pump inline doesn't seem to hurt the heating much if any. You may miss it next Winter when it's 20 below but otherwise I'd just unplug it and forget about it for now.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold