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I have three floors in my home. The bottom floor has its own gas furnace and the 2nd and 3rd floors share another gas furnace. Everything was working great until I added a NEST to the first and second floors.

The NEST works wonderfully on the first floor (own furnace).

The NEST won't turn the heat on on the second floor (shared furnace.) When I use the Honeywell thermostat on the third floor, the heat turns on just fine.

Can anybody point me in the right direction? Does this sound like a wiring issue? I've ruled out fuses because the heat works fine on the third floor. Is that a terrible assumption?

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Nest has a service to guide you to the proper connections when installing. Did you use them? – bib Jan 28 '14 at 22:04
Standard triage for a Nest problem usually includes a listing of the wires going to the Nest, a picture helps too! Can you provide that? Can you also tell us what wires are going to your 2nd and 3rd floor thermostats? Before you installed the Nest did the 1st floor thermostat also control the 2nd floor? – Freiheit Jan 29 '14 at 16:43
Nest therms have 100s of bugs and not-ifs. I would look on their forum for sharing thermostats. Might not work. Might have to be set up different. – DMoore Jan 29 '14 at 18:06
Does the furnace operate with the NEST? Have you tried pressing the front of the hea link? You will hear a click, if furnace doesn't start then it's wired incorrectly. If the furnace starts check you zone valve is operating, usually you can manually move these. As Freiheit said, wiring layout is required – w1ggan Jan 9 at 23:30

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