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I just hooked my Nest 3rd gen thermostat to my split heating/cooling system with a Common wire coming from the air handler in my ceiling. On my old stat I didnt use a common because it was battery powered. With everything hooked up my AC/fan is running fine but my heat won't kick on. I noticed that the Rh port shows "Power" greyed out and get a N72 error.

In my research it looks like this may be a common problem with split systems. Some people are still able to run their heat even with the error but for me I can't get the heat to run. Is this a wiring issue? Does the Heat have to somehow connect to the C wire from the AC?enter image description here

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  • Can you post the make and model of your air handler/furnace as well as photos of the wiring at both the thermostat and air-handler/furnace ends please? May 1 '21 at 1:29
  • does connecting W1 to RH start your heat?
    – Jasen
    May 1 '21 at 4:18

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