Water Pump Failure Question

[Texaspettey]

I just completed a flush and coolant swap on my 2001 GTS. After I filled with the new coolant, the temp runs right up to the red zone within 2 minutes just at idle. The heater is blowing cold air. That would signal a water pump failure based on my previous car experience. Is there another possible diagnosis? It seems odd that the water pump would work fine, then completely fail after just a flush. I would have expected it to fail gradually, first visible under heavier load. It isn't leaking and the system holds pressure just fine. Since water pumps are expensive and hard to find for Gen2, I'd like to get other options off the table.