How to wire Horstmann C-Stat 11-ZW wireless programmer to Worcester 24CDi?

Discussion in 'Plumbing and Central Heating' started by trionic, 30 Apr 2020.

  1. trionic

    trionic

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    In this thread you helped me to wire a Horstmann C7 to my Worcester 24CDi. That setup has been working well since then but now I must switch to a wireless thermostat because the programmer is now in the way of a book case.

    I have purchased a Horstman C-Stat 11-ZW.
    [​IMG]
    [​IMG]

    As with the C7, I am baffled with the wiring instructions and the existing wiring on the 24CDi.

    This is the wiring on the existing Horstmann C7:
    [​IMG]

    This is the wiring situation at the boiler end:
    [​IMG]
    [​IMG]

    The junction box wiring is messy because the box as originally fitted had to be changed.

    There is a isolating switch not shown in the photograph. T&E runs from the isolating switch to the white connector box to the left of the first photo and out of the box runs a white flex. This disappears into the wall. Connected to the junction box is T&E as shown and a white flex.

    I did measure voltages at the programmer and boiler ends but the results didn't help my understanding.

    This is the wiring back plate of the C-Stat 11-ZW:
    [​IMG]

    The installation manual is here (PDF) and these are the wiring diagrams:
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]

    I know that this should be simple and I have an idea of what I should do but not enough confidence to proceed and I would rather ask for help than blast ahead and damage equipment or myself.

    Thank you for your help.
     
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  3. CBW

    CBW

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    Red wire from Programmer to L on new prog room stat
    Blue wire from Programmer to N on new prog room stat
    Call for heat (yellow) to 4 on new prog room stat
    Fit a link wire between L on new prog room stat to 2 (common) on new prog room stat
     
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  4. trionic

    trionic

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    Mental. How did you work that out :)

    Great - I'll follow your directions and report back.
     
  5. trionic

    trionic

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    Ahhhh I think I may have mislead you but omitting vital information.

    Because the existing C7 is in the way of furniture, I intend to remove it entirely, disconnect the T&E from the boiler end and leave the de-energised cable in place. The new C-Stat 11-ZW receiver would be installed at the boiler end. Am I correct then in thinking that:

    Brown wire from boiler white flex to L on new prog room receiver
    Blue wire from boiler white flex to N on new prog room receiver
    Call for heat (black with red sleeve) to 4 on new prog room receiver
    Fit a link wire between L on new prog room receiver to 2 (common) on new prog room receiver
     
  6. ericmark

    ericmark

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    Replacing the junction box
    Brown = Line feed = L and Com on new thermostat, needs link wire.
    Black = Call for heat = 4 on new thermostat.
    Blue = Neutral = N on new thermostat.
    Green/yellow = Earth bond = Brass earth terminal on new thermostat.
    The triple and earth wire now redundant.
    As to if you actually have enough cable to mount proper not so sure.
     
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  7. trionic

    trionic

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    Thank you, No, not enough slack in the cable to mount so I'll have to extend those. I have some 3-way Wago connectors but I might buy some splice connectors and house them in a gel box (I think).
     
    Last edited: 1 May 2020
  8. CBW

    CBW

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    Looked at the instructions for a combi, then worked it out from there. I’m slowly learning on the electrical side (I’m a plumber with my gas by trade ).
     
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  9. ericmark

    ericmark

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    If you can't replace the cable due to it would disturb some gas seal, then would look at the lighting junction boxes as they have cable clamps in them.
     
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  11. trionic

    trionic

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    So today I undertook this work but the receiver did not power-up. I checked the wiring and it was as per the instructions.

    I extended the white flex with triple & earth, with the grey conductor used as neutral and sleeved blue.

    The receiver end:
    [​IMG]

    Wiring under the boiler with junction box removed:
    [​IMG]

    Wiring under the boiler with new cable to receiver connected:
    [​IMG]
    (I'd already bought the knock-off Wago connectors before I received the recommendation for the lighting junction box: I'll sort out a box of some type to house the connectors).

    Switched the ring main back on and the receiver did not power up, so I took some measurements with the meter.

    At the receiver end:
    Live/neutral = 2.2v
    Neutral/black = 12.9v
    Live/black = 168v​

    Disconnecting the receiver wiring and clipping onto the white flex:
    Live/neutral = 9.6v​

    Now I am a bit stuck.
     
  12. trionic

    trionic

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    In the last picture in my previous post you can see a white rectangular junction box. Inside are three Wago connectors, splicing together a 240v mains supply T&E to the white flex which disappears into the wall. I tested the supply into the box and it was 240v. I tested again the other white flex and across live and neutral I measured 17v (it was 9.6v before) and I got the same 17v reading on two different meters, both with new batteries.

    What's odd is that the C7 requires a 240v supply on terminals 1 and 4 and that's brown and blue on the flex so why 240v isn't measured across those live and neutral conductors now I cannot fathom.
     
  13. trionic

    trionic

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    I connected the old C7 in place of the new receiver and it works fine, so although the C7 installation instructions say that it requires a 240v supply, it clearly does not.

    I propose to take a T&E 240v supply from the isolating switch to N and L of the receiver and then connect black from the flex to terminal 4 of the receiver. Leave the white flex neutral and live terminated and safe. Connect all earths.
     
  14. CBW

    CBW

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    ^^^^^^Might be a good idea. However, before you do, did you try my of this with the boiler turned on? Also your c7 is battery powered, so it just switches the live in and live out.
     
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  15. trionic

    trionic

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    The measurements were taken with the ring main on and the boiler switched on but not fired-up on either HW or CH.

    The difference I think is that the C7 is battery powered (even though the instructions says that it required a 240v supply on a 3A fuse), while the C-Stat is not battery powered. That may be why the C7 works without the 240v supply and masked this problem.

    I think that without a permanent 240v supply, the C-stat won't power-up at all.
     
  16. CBW

    CBW

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    Yes this is correct, the c7 is battery powered, I didn’t download the instructions yesterday (my bad). It didn’t mask anything, it just switched the live in and out. Again what is my bad, the c-stat does require a permanent live and permanent neutral, and the switch out without a linked common, as you could use the live from old stat, which would be the red, and switched out (number 4).
     
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  17. CBW

    CBW

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    Please ignore the part on post #12 regarding turning the boiler on. Pay more attention to post #14.

    Cheers.
     
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