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I have a oil burner for baseboard heat and forced air AC that is controlled by one thermostat. There are a total of 5 wires coming to the thermostat 2 wires from the boiler and 3 wires coming from the AC. I want to to replace the thermostat with Honeywell wifi thermostat that requires a C-wire. My current wire is a 5-wire. Assuming that I will be able to pull a new 6 or 7-wire to the thermostat my question is where do the connect the other end of the C-wire. Can I connect it to the boiler? Do I need 2 C-wires one each for boiler and AC? wiring at boiler wiring at air handler

The boiler is Buderus G115WS/4.. It has 3 zones. Zone 1 for first floor, zone 2 for 2nd floor and zone 3 for hot water.

A/c handler is Carrier model FX4ANF030

At the thermostat Red -> R Blue -> Rc Green -> G Yellow -> Y White -> W

  • In you situation, it's probably going to be easier to grab C from the A/C. However, there's no way to say for sure, since you've told us almost nothing about your setup. Please include make and model of all equipment, and possibly a wiring diagram showing the current wiring. – Tester101 Apr 6 '17 at 21:59
  • I attached pictures and updated model numbers. Hope this gives a better picture. I do see the option to connect C to the boiler zone 1. Will this work. – U Reddy Apr 21 '17 at 1:38
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    You should be able to connect a wire from the C terminal on the zone controller, to the C terminal on the thermostat for that zone. For example, if the new thermostat is the zone 1 thermostat. You'll connect the c wire to the zone 1 C terminal on the controller, and the C terminal on the thermostat. However, sometimes with boilers and zone controllers, things aren't always wired exactly how you'd expect. To get a definitive answer, you'll have to include a wiring diagram that shows all the control wiring between all the equipment and thermostats. – Tester101 Apr 21 '17 at 10:31

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