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Help with Honeywell TH8320WF

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adambnyc
adambnyc Member Posts: 260
Hey, friend of mine gave me this thermostat and I’d really like to get it working. Manual shows a bunch of different wires needed. I only have two wires for my current thermostat, probably just for open and close circuit. I’m guessing I need to supply 24v or something to this. Can I come off the boiler thermostat for this?

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  • adambnyc
    adambnyc Member Posts: 260
    edited January 2018
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    Correction, I have three wires to my current thermostat, one not in use
  • adambnyc
    adambnyc Member Posts: 260
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    Do I just need to connect the wire not in use to one of the wires not in use on my boiler transformer? And connect that to the “C” common on the thermostat?
  • adambnyc
    adambnyc Member Posts: 260
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    Alrighty... my face is a little red on this one. I did just as I “thought” would have worked. Connected the unused thermostat wire to an unused lead coming from my boiler 24v transformer.....

    Turned the power on expecting to run up stairs and see the thermostat working... that didn’t happen.

    Was greeted by that familiar “PCB Burning” smell. So I ran down stairs only to be greeted by that “burned out transformer” smell.

    Pretty annoyed. I have a fused transformed for this very reason! It never popped...just burned... and now I’m sad.

    Thank god I had a spare or I’d be running out to get a part for my own no heat call.

    Lesson to myself “Adam,,,, when it’s the dead of winter, regardless how bored you get, regardless of how many things your trying to avoid that your wife wants you to do.. DONT SCREW WITH THE HEAT!

    Appreciate the “here’s were you went wrong” direction on this one
  • adambnyc
    adambnyc Member Posts: 260
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    I think I figured out where I went wrong and it makes a lot of sense, I provided the 24v common, but I didn’t give it a neutral via the Rc lug, which I guess stands for return common? No idea why this would have caused the transformer to blow out. Maybe the old wire that I was using grounded out some how.

    I was reading that someone setup a totally different transformer, I don’t think that I need to do that. Why can’t I just tap into the existing 24v that’s already on the boiler, (btw, I upgraded it to higher capacity)
  • ratio
    ratio Member Posts: 3,652
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    NO!

    The RC & RH are both hots from the transformer, often jumped together but it depends on the system. The C is the common, it must come from the RC transformer.

    Here's the manual for that stat. The wiring diagram is on page 3 (such as it is). You want the hot on RC & RH, the common on C, I the heat call on W as shown on the "conventional" side of the terminals.

    It's quite possible that one of the conductors is shorted out. Do you have a multimeter of some kind?

  • adambnyc
    adambnyc Member Posts: 260
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    I’m awaiting a new transformer and also, I’m pretty sure I need more than just the 3 wires that I have. I’m going to run new thermostat wire.

    I’ve have a multimeter.

    Thanks for the input!!!
  • adambnyc
    adambnyc Member Posts: 260
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    Where should I connect the “c” wire to the transformer? Should I put it on the common coming into the transformer?
  • ratio
    ratio Member Posts: 3,652
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    If you have only one stage of heating and no cooling controlled by that stat, three wires will be enough. After you take a few pics and/or label the wires, take them loose on both ends, and using the meter set to "continuity" (or a low Ω range), check the wires between themselves, and ground, for shorts.

    How many wires are on the current transformer? There will be at least two, but there may be more. In any case, set your meter to AC volts, 50-100 volt scale if not autoranging. Go from each LOW VOLTAGE terminal to ground, you should show one terminal with 24-27ish volts and one with 0-2ish volts. The first one is the hot, lands on the RC/RH terminal (leave the jumper installed). The second one is the common, or 24V return, it'll land on the C terminal. The third wire, the one that goes to the boiler/gas valve/whatever, will land on the W terminal.

    Nothing that connects to the stat will connect on the high side of the transformer.