Need help with clotted catheters??

Our local hospital inserts Groshong PICC by Bard which we have no problems with and they do not require heparin. Another hospital which we receive referrals from inserts Cook PICC's which seem to clot quickly whether the patient is on an infusion pump or doing IV push. We are using 100u/ml heparin 3cc as final flush. Our team can not figure this one out and our pharmacist believe it is the type of line. Anyone else seeing this problem? Thanks for any help.