This is a bit of a long shot, but while you're at it you may as well check that the variable resistor (or potentiometer) on the power valve motor assembly is working correctly.
If you put an ohm meter across the LightGreen and Green/Blue wires I think the resistance should vary from approx 5-8 kohm as you turn it.
Likewise, if you put an ohm meter across the LightGreen and White/Red wires the resistance should vary a similar amount but in reverse.
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