Easy fix for clogged heater core.
Get your old bike pump, cut the connector from the end of the hose. Remove the coolant line from the output side of the heater core under the hood. Stick the bike pump hose in the heater core where you disconnected the hose and pump it a few times. It breaks loose the clog and if your lucky it stays that way. It's kind of clumsy to do, you may need 3 hands but it works.