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I am replacing a fan-coil thermostat. Unit itself is Wito ultra-s 06-2t. Old one was wired and installed by an electrician, quite some time ago. I dismounted the old one and wanted to replace it with the new one, but it appears that there is a "COM" contact on a new one and nothing similar on the old. I'm quite inexperienced in wiring so I'd like to find out:

  1. Whether wiring a COM is required for the thermostat/some of its features to work
  2. Whether ignoring COM contact is safe
  3. Whether there is any wire in the current setup (probably, one of the blue ones in the N slot) that should go into the COM contact

Old: old

New: new

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    I'm guessing that one of the blue wires that are doubled up is a COM (constant 24v) supply. Have you checked that? If so, that would move over.
    – isherwood
    Jul 13 at 20:50
  • I don't have an indicator screw, guess i need to get myself one to check that.
    – HardLuck
    Jul 13 at 20:55
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    A what now? I recommend any homeowner purchase an inexpensive multimeter.
    – isherwood
    Jul 13 at 20:57
  • Or that, yes, thank you for you input! At least i have faith that it'll work now!
    – HardLuck
    Jul 13 at 20:58
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    this unit does not have 24 volt
    – Ruskes
    Jul 13 at 21:44

1 Answer 1

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Jumper N to COM

From the wiring diagram on your new unit, it shows the COM terminal connected to the incoming mains neutral, so you should simply connect suitably sized wires from COM and N on the new thermostat to the mains neutral connection coming into your box with a suitable wire connector for your location.

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6
  • So you are suggesting to change the wiring on the fan-coil unit? Or am I interpreting your answer wrong?
    – HardLuck
    Jul 14 at 22:57
  • @HardLuck -- no, the jumpering I'm talking about takes place at the thermostat
    – ThreePhaseEel
    Jul 15 at 1:15
  • I've tested blue wires with a multimeter, they are both zeros. To be perfectly clear on the course of action I: 1) jumper 1 and 7 2) wire 2:yellow, 3:green, 4:black, 5:nothing, 6:brown, 7:2x blue, 8:red. Is this correct?
    – HardLuck
    Jul 15 at 23:58
  • @HardLuck -- if the terminals on the device are rated to accept two wires, then your plan is fine
    – ThreePhaseEel
    Jul 16 at 0:42
  • any way i can verify that? Nothing about that in the user manual.
    – HardLuck
    Jul 16 at 0:45

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