Originally Posted by Clavurion

That stratification flaps only works as heater core bypass affecting only the face vents. When the flap is closed all vents get the same air thru AC evaporator core and then heater core. If the flap is opened the air for face vents gradually bypasses heater core.

If temp setting is on min. the water valves should close the circulation to heater core. You can test if the hoses on the firewall are warm which they likely are. All pointing to failed heater valves or the control voltage from IHKA. (The valves are open on rest state.)