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Using 24VAC Louver for C-Wire

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I'm looking to install a wifi thermostat on my boiler, however I don't have a C Wire running from it. I do see a place for a "24VAC Louver" with nothing connected to it. Can I use this terminal for it? Thanks.

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  • Jamie Hall
    Jamie Hall Member Posts: 23,655
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    Without a circuit diagram, it would be hard to tell -- but I'd be really surprised if that pair of contacts were either hot or gound...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EdTheHeaterMan
  • 109A_5
    109A_5 Member Posts: 1,388
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    Hello @lew21,
    What unit is this Make / Model ? Wiring diagram ? If the R/W uses 24VAC (most likely) where is the 24 VAC transformer ?
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • HomerJSmith
    HomerJSmith Member Posts: 2,511
    edited April 2023
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    I'm not sure how your Lochinvar is wired, but there is a electrical diagram on the cabinet door.

    What you need to do is to take a volt meter set to 24 V ac and touch one probe to the common wire from the wifi thermostat and the other probe to either screw 4 or 5 the louver screws on the connection board, your photo. If the screw shows 24 V ac on the meter, the answer is yes. Choose the screw that has 24 V ac. If the meter shows 0 V ac on either screw the answer is no. Leave the jumper in place if it has a jumper.
    On the Lochinvar there is a transformer with a Yellow lead and a Blue lead. The Yellow wire has a 3 amp inline fuse. The fuse is hidden behind the control board panel on the wall hung where the wires goes thru the hole in the metal and in the Knight under the control board toward the rear. I can see that your boiler is a Knb (Knight) . I think that the Blue wire from the transformer is the common and the fused Yellow wire is the 24 Vac out. You could make a connection to the Blue wire with a inline wire splice you can get at any auto parts store. It would allow you to tap into the Blue wire with out cutting it.
  • HomerJSmith
    HomerJSmith Member Posts: 2,511
    edited April 2023
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    You can also, using a meter set to 24 Vac, put one lead on the louver 24 V screw and the other lead of the meter to the 19 or 20 screw and see if you have 24 Vac. You should have 24 Vac on the 19 screw if the louver screw is a common connection. You can touch one lead of the meter to a metal spot on the cabinet and the other to the 19 or 20 screw. It would show you which screw has the 24 Vac to the thermostat from the transformer. It is probably R screw 19. If you touch the louver screw and the metal cabinet you should get 0 vac.

    You can buy a cheap digital meter at Harbor Freight or Home Depot. Harbor Freight Home Depot

  • HomerJSmith
    HomerJSmith Member Posts: 2,511
    edited April 2023
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    You also have a common connection on the Low Water Cut Off connector, but there isn't any connector pin in the slot and would have to be added. Probably above your ability. You would need a Molex Mini-fit Jr female connector placed in the correct hole in the nylon connector. You can get Molex Mini-fit Jr connectors on Amazon.


  • Big Ed_4
    Big Ed_4 Member Posts: 2,832
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    The low water plug is a series circuit .

    Just from your photo , It's a single zone system and your thermostat is connected to "Heat/Loop demand" . Install a relay , a relay with a fuse before the boiler . Most of the wall relays have a common and fused . Separate the wifi from your board

    There was an error rendering this rich post.

  • 109A_5
    109A_5 Member Posts: 1,388
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    You could make a connection to the Blue wire with a inline wire splice you can get at any auto parts store. It would allow you to tap into the Blue wire with out cutting it.

    I would not recommend "Scotch Lock" wire taps to anyone, unless you want an intermittent connection down the road. I've seen too many problems with them.
    Big Ed_4 said:

    The low water plug is a series circuit .

    Yes the control side wires are. However a 24 VAC powered Electronic LWCO needs power. So the C-Wire may be effectively be there at that connector. The issue there is getting the correct pins, and if you don't have the correct crimping tool you can fold the tabs over and carefully solder them, but that is not for most folks.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
    HomerJSmith
  • Big Ed_4
    Big Ed_4 Member Posts: 2,832
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    Oh ... The power is the other empty prongs ? I see thank you

    There was an error rendering this rich post.

    EdTheHeaterManHomerJSmith
  • 109A_5
    109A_5 Member Posts: 1,388
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    Hello @lew21,

    Maybe off topic but is the white outdoor sensor wire connected correctly ? It looks a bit cattywampus.


    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
    kcopp
  • Big Ed_4
    Big Ed_4 Member Posts: 2,832
    edited April 2023
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    It was skinned but not cut . End of the day job . Looks like they went high on the clamp . Good catch....

    There was an error rendering this rich post.

  • TonKa
    TonKa Member Posts: 104
    edited April 2023
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    My SWAG is a "24VAC Louver Relay Coil" probably only has power when the unit is trying to satisfy a call. I'd be a bit surprised if it fulfils your need for a C wire. A voltmeter will tell.

    What does this board do for your boiler? It's got jumpers on the stuff normally used to keep things safe.
  • HomerJSmith
    HomerJSmith Member Posts: 2,511
    edited April 2023
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    What does this board do for your boiler? It's got jumpers on the stuff normally used to keep things safe.
    It's a connection board that connects the inputs to the control board which runs the boiler.

    The jumpers are there because like Big Ed said the ladder wiring of safety devices is in series and without the aux devices like a louver connected to the board the jumper keeps the boiler display from faulting out.
  • TonKa
    TonKa Member Posts: 104
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    What does this board do for your boiler? It's got jumpers on the stuff normally used to keep things safe.
    It's a connection board that connects the inputs to the control board which runs the boiler. The jumpers are there because like Big Ed said the ladder wiring of safety devices is in series and without the aux devices like a louver connected to the board the jumper keeps the boiler display from faulting out.

    Perhaps I wasn't clear. I get what a jumper does. What I don't get is where all your safety devices are and, if they are wired in somewhere else, what's the point of this board?
  • HomerJSmith
    HomerJSmith Member Posts: 2,511
    edited April 2023
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    What I don't get is where all your safety devices are
    The safety devices aren't there which is why you need jumpers to fill that space (connections). It's like the GAS PRESSURE SWITCH connection, you have to add a gas pressure switch to the gas line. Then the boiler could monitor the incoming gas pressure and shut down if the gas supply dwindles.
    There are some safety devices built into the boiler, too. Sensors, etc.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,167
    edited April 2023
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    @TonKa asked: What I don't get is where all your safety devices are
    There is a difference between Required safety devices and optional control devices. Gas pressure switch is not required. If you have LP and the tank gets low and the pressure drops, you SHOULD use a low pressure cut out to keep the burner from operating. My guess is they are connected to natural gas. If you have a confined space and a louver must be open for combustion air then you don't want the burner to operate if the louver is closed. If you don't have a confined space problem, then you don't have a louver and therefore no need for a louver or louver proving switch. If you don't have a run time clock then there is no need for wires to be connected to the run time contacts. If your system does not have a flow switch then there is no flow switch to connect.

    The reason all these different contacts and terminals are there makes this control work on many different systems. But you can jump out any input that is not "the minimum required" and leave any alarm type contact disconnected if there is no alarm to connect.

    Kind of like using a Heat/Cool thermostat on a 2 wire heating only boiler. I'm thinking that you don't question why anyone does not connect the G or the Y to that heating boiler. The reason is obvious, the boiler does not have fan or a cooling relay. The apprentice might ask why did you only connect the R and the W and leave the G and the Y terminals empty? The experienced one already knows. ... and the idiot would waste time and money to return to the supply house and say you gave me the wrong thermostat. I need one that has only R and W.

    I, for one, would use the universal control to save travel time and have less inventory cost per service vehicle.

    Just some rambling thoughts from an old fart

    Mr. Ed

    Edit: PS. I'm going out on a limb here... I bet there is no low water cut off on this system.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,167
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    109A_5 said:

    Hello @lew21,

    Maybe off topic but is the white outdoor sensor wire connected correctly ? It looks a bit cattywampus.


    Do you thing it might be shorted? or is Cattywampus a technical term?

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • HomerJSmith
    HomerJSmith Member Posts: 2,511
    edited April 2023
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    Cattywampus

    Ed, it's an industry term. It's like a Therman Wire. When I'm ask why the boiler wasn't working, I always tell the customer, it was a failure of the Therman Wire. A term from Mad Magazine.

    The irreverent humor of Mad Magazine was the delight of every young male. Females never got the humor.

    Just yesterday, I was looking at a boiler with a problem and I said, "There is nothing I don't know about boilers, everything there is to know about boilers, I know." Then, looking it over, I said, "How do you turn it on?" The guy got the humor and commented on it, but the gal didn't get it. Sometimes life is so much fun. It turned out to be a squealing induced draft fan.

    At first, I thought the squealing was bats in the chimney, I wonder where I got that idea, hmmm, but, alas, there wasn't a chimney.
  • HVACNUT
    HVACNUT Member Posts: 5,890
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    I wouldn't power a wifi thermostat through the boiler circuit board. Isolation relay for sure. 
    kcopp
  • HomerJSmith
    HomerJSmith Member Posts: 2,511
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    Yes, a relay would certainly be safer. The lochinvar transformer has a 3 amp fuse. Blow the control board and that is big buckos. Something to definitely consider.
  • JUGHNE
    JUGHNE Member Posts: 11,109
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    I talked to Lochinvar tech support about where to get a common connection for tstat.

    He replied that Lochinvar did not want any use of the common for tstat.

    So a transformer/relay would have been needed to obtain a common.
  • HomerJSmith
    HomerJSmith Member Posts: 2,511
    edited April 2023
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    Wire a relay to the Wifi thermostat this way (safest). Use the following relay on a 4X4 metal electrical box. Connect a plug-in electrical cord to the black and white wires on the relay transformer. 16 gauge will do and plug it into an electrical outlet. Walla, simple. https://www.supplyhouse.com/White-Rodgers-90-113-Fan-Control-Center-120-VAC-Primary-24-VAC-Secondary-SPDT-Relay



  • Big Ed_4
    Big Ed_4 Member Posts: 2,832
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    I would step up the relay with one that is fused if a common is used...

    There was an error rendering this rich post.