I believed I tried everything and the heater still blows cold air. Here's what I did so far. 1) Made sure the heater controller moved the heater valve open and close positions. That was working. 2) Checked thermostat is was working. Replaced with a new 1 any way. 3)Disconnected the heater core inlet and outlet hoses and connected a water hose directly to the heater inlet. Turned on water to see if the core had a blockage. Water was coming out the outlet hose. 4) Bled radiator. I did a H22 swap a year ago I had this prolem with the old engine too. Need help winter is coming fast I need heat.