Why don't my heater get hot

It could be a number of problems that can keep you from getting heat. Like junior said, a plugged or partially plugged heater core, the water control valve, or the flaps, servos, blend door controls in the heater suitcase. You can make it like a non-A/C car and remove the water control valve and run hot water through the heater core all the time. You'll still have to get the controls for the heater suitcase working though so the correct flaps open. They're run by vacuum lines and servos so the push button control needs to work you you'll have to bypass it and manually open the right ones.