Heater doesn't work

Hello, before you "do", inspect. Is the hose going into the heater core hot and the hose coming out cold? If so, then yes -- you may have a heater core restriction. If the temperatures are the same -- then check beyond that. You may find that there is a climate control issue within the plenum that is preventing the flow of hot air inside the vehicle. You may find the temperature of the coolant never gets hot enough to give you the heat you need. Perform needed testing before "doing" because you could actually complicate matters more.