how do i remove the coolant pipe?

[pgrobin]

I'm trying to remove the coolant pipe on my 1996 Passat VR6. It is the pipe from the pump to the other end of the engine, it connects into the thermostat housing.

I've got the housing off, and have removed the hose from the pipe. But while I can twist the pipe it will not come away from the pump. Is this just stuck, or have I bitten into a much more difficult job than expected?

Thanks in advance for any assistance.