No heat - what's next?

Smallest channels for coolant to flow through are in heater core. Thermostat can also get blocked by the stuff.

Flushing out the system or parts of it might be better than just replacing parts. And of course it's a lot easier to flush parts like heater core than to replace them. A new thermostat gasket might be needed when reinstalling the thermostat so it might be worth to replace the thermostat and gasket. Flushing is best if done part be part like first just a heater core (and hoses) bacwards and forwards).

Now that you have those parts out and you do know that stuff is blocking the system you could try and check what it's. Maybe some sort of cleaner could be used? If it's leak fix then it might not even be possible and you might need to replace at least the heater core.

Coolant not circulating properly is either a bad thermostat (probably blocked by that stuff) or air in the system (bleeding blocked system can even be impossible).

Head gasket has cylinders coolant and oil going thought it. If coolant doesn't have oil and oil doesn't coolant in it then what's left are leak between cylinder and coolant (leak between cylinder and oil is not really possible). Leaking coolant into cylinder would probably cause hard start. So what's left is leak from cylinder into coolant. Ways to test are either just trying to see how fast pressure builds up after start or to use tester that tests the coolant for exhaust gas to see if head gasket failure.

 

did you get it working? im going through the exact same thing. Found the same clogged heater pump.

 

Did you sort yours out I am having intermittent heat issues now too

 

Apologize for the delay . You have me stumped. There is a sensor on the thermo tank.

 

The diagram is wrong. Feel the hoses.