Can't turn heat off????

Hey folks! I have a 1984 528e that I can't turn the heat off. I pulled the heater valve and it appeared clean and unstuck. I also carefully applied 12 volts to it and the plunger did actuate in then out?? I cant seem to stop the heat coming from the defroster or floor vents and the sliders and doors are connected and working too. Please help!

The electronic heater valve which is fitted on the bulkhead has failed which is a very common problem, Other symptons are the inabilty to regulate the hot air or cold air above or below 60 mph.