central line flush/lock

I maintain a central line..we do flushes with 10cc BNS and lock it with 300units of Hepalean on a weekly basis..everytime my client goes into hospital they say we only use NS daily to keep the line open...but we were always told to lock it with the heparin solution...any others out there maintaining central line patency. This line is not used except for when IV meds or fluids are needed...he has bad veins so IV access is neart impossible. We have done it this way for 8 years!

Thanks

Theresa