So I had a radiator leak and put some BARS stop leak in. Heater is not working and I think I clogged it with the stop leak. I replaced the radiator and fluid. Is the anyway to maybe flush that stuff out of the heater core or is it just screwed and I need a new one.

 

Try taking the hoses off that go to the core and spray some water with a garden hose through there, just be careful the heater core cant stand much pressure (7-8) PSI