Send it in, this could be caused by one of two things, if it is a pump from early 2007 it could be a manufacturing defect, if it is a pump from any other series it is more likely to be calcium build up but when locked solid they are difficult to remove.
Tunze USA
305 Victor St
AustiN TX 78753
Usual turnaround is 24 hours after receipt. Please include a return address and phone number.