I have a 2006 Audi A3 and had a timing belt water pump changed out about 5,000 miles ago with the water pump as the dealer was in there changing the intake camshaft under an extended warranty. Turns out the OEM water pump had a failure, it looks like woodruff key on the impeller ( there is one) sheared as you can rotate the impeller freely with respect to the gear.

Has anyone heard of this or seen it? I cannot find anything in the forums.

When you rotate the gear the impeller will rotate too, but if you put any resistance on the impeller it will stop. Unit is 2 years old max.

 

pics attached.