No Heat

I've 528e bmw 1988 model. Have problem with heater, it does not work. It was working couple of months ago untill I replace the throttle body due to leak from the throttle body cover. I had already check and
replace the heater valve with used one. Need the heater to be working since winter is just around the corner. How do you know if the heater valve is working good? Any advice ....
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on about something:

First check your coolant level. Make sure you haven't got an air lock in the system, there is a bleed plug (don't ask me where, I don't have a 5 series, but there was another thread on here a couple of weeks ago about it). The heater matrix is one of the highest points in the system, so it's the first thing that shows low coolant level.
Dodgy.
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The control signal to the heater valve is a low frequency square wave. It's duty cycle controls how much heat you get. Stick a test lamp or meter on the heater valve connector. You should be able to vary the on/off ratio of the control input by playing with the heater dial.
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