Coolant not flowing to heater core/heater does not work?

The heater has been giving me issues for a while now. At first the heater wouldn’t put out heat unless driving down the road. Now it doesn’t work at all. A/C and blower and blend door work fine. I thought it was a clogged heater core because one line was warm and the other cold. I pulled both lines, and the heater core wasn’t clogged at all. Water flowed through easily both ways. Then I put a jumper hose connecting both heater core hoses and no coolant is flowing through. I also changed the thermostat and bled all of the air out of the system. Still has no coolant flow through those heater core lines. The engine runs great, no overheating and upper and lower radiator hoses get hot.