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c-wire

rickb54
rickb54 Member Posts: 2
Which terminal would I connect a c-wire to on a Honeywell L7224 aquastat?

Comments

  • Looks as though they don't give you an available "C" terminal.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • HVACNUT
    HVACNUT Member Posts: 6,162
    rickb54 said:
    Which terminal would I connect a c-wire to on a Honeywell L7224 aquastat?
    You don't. 
    What are you trying to do, WiFi thermostat?

  • Teemok
    Teemok Member, Email Confirmation Posts: 667
    If I really needed a C terminal from that control board I could get one. There is a way to tap off the transformer directly. Most people are not be that adventurous but it can be done. You could use a relay board in between and it would have a C terminal for you on it.
  • Teemok
    Teemok Member, Email Confirmation Posts: 667
    edited October 2023
    You would need a 120v outlet you can plug into and a light gauge appliance pig tail, some 2 wire thermostat wire and a romex connector or two. See "typical wiring" in the instructions and ignore the circulator wiring part. The 24v terminal that is next to R and W is the C terminal.

    https://www.supplyhouse.com/Taco-SR501-4-1-Zone-Switching-Relay?utm_source=google_ad&utm_medium=pmax&utm_campaign=pmax_best_sellers&gclid=EAIaIQobChMIq8P1-rzigQMVXwOtBh2wDAMtEAQYASABEgLmufD_BwE
    Alan (California Radiant) Forbes
  • rickb54
    rickb54 Member Posts: 2
    Yes, I need a c-wire for a wifi thermostat
  • Jamie Hall
    Jamie Hall Member Posts: 24,382
    You can't get power from an aquastat. It's a switch, not a power source. Depending on the rest of your wiring, there may be a way to connect from the system transformer and get a C (common return) wire. If you have a relay board, as @Teemok suggested, you may be able to get power from that.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Teemok
    Teemok Member, Email Confirmation Posts: 667
    edited October 2023
    The straight forward route is spend money and assemble the kit above. Or for almost free you can hack: Obviously electricity is dangerous. If you have no knowledge or experience get some help from someone who understands the following. One of the 4 connections of the transformer is the C wire. 2 are obviously not it being 120v hot and neutral. Figuring out which of the two low voltage points is + is the trick. There might already be a fuse in on the R side of the TT circuit. If not you can put an inline fuse on the C wire. If we rename the T T terminals R and W, R being the + You just need a wire soldered to the C terminal of the low voltage side of the transformer Or easier, the C is technically ground. "IF" you know which terminal is R (+) macke sure it is connected to the R of your thermostat the other T will be W. You can power the thermostat by grounding your thermostats C wire to the chassis ground of the control board. R to ground will measure as 24v ac. W to ground has no voltage difference. C is the wifi t-stats way of charging by (completing the circuit R to ground) without sending voltage through the W terminal. When your thermostat "calls" for heat it closes a switch that sends R power to the W and that activates the boiler control. Charge current without control activation is your goal.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,011
    I can't be sure because it has been a long time since i did this but I once pulled one of those apart and looked on the back of the circuit board. I believe that the T terminal that is also marked 3 is R and terminal 3 is Common while the other T is W. Just a guess at this point because I wanted to know the answer to that same question years ago. File this under the forgot part of: "He forgot more about Oil Heat that you'll ever know"

    Not a very powerful transformer, so I'm not sure if there is enough power for more than one extra piece of equipment like a thermostat. Depends on how much power your thermostat is drawing

    Edward Young Retired

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

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,201
    That is an electronic aquastat. You not getting a c terminal off of it.

    If you want to add an additional transformer and relay you can do it. and get a common terminal

    See the attached drawing.
  • Teemok
    Teemok Member, Email Confirmation Posts: 667
    edited October 2023

    That is an electronic aquastat. You not getting a c terminal off of it.

    If you want to add an additional transformer and relay you can do it. and get a common terminal

    See the attached drawing.



    Don't believe the C side of the 24v transformer on that board is grounded? I suppose Honeywell might not do that so the only C is the solder point of the secondary coil of the transformer, it is there. I didn't believe it either until I proved it. Every blue wire in a Trane furnace control is ground to the cabinet. Similar to how all 120v neutral / white wires are grounded at the breaker panel.

  • Teemok
    Teemok Member, Email Confirmation Posts: 667
    The power draw to charge a nest, ecoee or the likes capacitor is tiny.
  • Jamie Hall
    Jamie Hall Member Posts: 24,382
    edited October 2023
    @JohnNY posted a very simplle diagram as to how to go about wiring up a wi-fi thermostat. You can find it here: https://forum.heatinghelp.com/discussion/193709/the-last-word-about-c-wire-thermostats-and-wiring-diagrams#latest VERY simple. Just do it and quit messing around with trying to make fancy boards do what they aren't meant to do.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Teemok
  • Teemok reminds me of icesailor, except on quaaludes. Super smart, but polite. I'm a fan!
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
    EdTheHeaterManTeemok