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Hello, I just saw your question, I am working on it. Tell me about how old your system is, so far it sounds like zone control board might be going bad.
If it worked earlier, the polarity is probably OK.
Please attach a well focused, close up photo of the zone control wiring diagram glued inside the service panel, the picture needs to be taken from straight on, in very good light.
You can use the paper clip- icon at the right end of thetool bar at the top of this dialog box to attach it here. ,Include a picture of the thermostat wire connections to the printed circuit board in the same area.
If there is no paper clip-icon, look for the '+attach files' link at left of your send button.
I can mark it up with trouble shooting instructions.
Hello, as a rough initial guess, I would say that this is some sort of electronic glitch due to use of Nest thermostats which may not be compatible with some variable speed furnaces.
Solving that problem is going to a very sharp controls man, on site with instruments.
If you can send me a photo of the zone controller with the wiring in place I can look it over for you however. We might get lucky.