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Worcester Bosch 40Cdi - wiring new thermostat

Discussion in 'Plumbing and Central Heating' started by pt44, 12 Mar 2013.

  1. pt44

    pt44

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    Hi - my 40Cdi has a wireless optimiser thermostat. I want to replace this with a fixed hard wired thermostat. I presume that this only needs 3 wires - one of those being an earth - so essentially 2 wires. Which terminals should these two wires go to inside the boiler?


    Seems like I have a choice of Ns, Ls and LR

    The wire you see is for my underfloor heating. That comes in from a separate wiring centre. I'm not sure it's actually wired correctly, as at the moment, I have to have the wireless thermostat on and the u/f on for both to work. They won't work independent of each other (as they should ideally). If anyone can tell me how that should be wired, that would be helpful.

    Thank you Paul
     
  2. boilerdoktor

    boilerdoktor

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    ls is live supply to stat and lr is switched live back to boiler to fire it up
     
  3. picasso

    picasso

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    You would need to trace the wiring from the wiring centre to connect a stat to the ufh, the wiring you have posted a picture of is the switched live probably from a couple of 2 port valves.
     
  4. pt44

    pt44

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    Sorry - maybe I wasn't very clear. I am NOT putting in a stat for the u/f. It already has one installed. There are two parts to my original question.

    1/ in my current set-up, I think I have things wired wrong. The wiring in the u/f side is fine in the wiring centre, but where it connects to the boiler, I think I have that part wrong. Hence why it won't work unless the rad side is also working. The image shown is the inside of the boiler. The brown wire is s/l from the wiring centre and the blue is the N. I've got them installed as shown on Ns and LR - but I think this may be wrong.

    2/ If I install a new wiring centre (not replacing the u/f one) adding just by my boiler. Then the wire that will come from the new stat (rads stat) will go to new wiring centre - but then what does it connect to at boiler end? Presumably - it connects in the same way as question 1.

    So I will then be able to re-wire the u/f wire and instead of going into the boiler, it can also go to the new wiring centre along with the new thermostat. Then they will both connect to boiler - and I will be able to work both individually. That's the plan.
     
  5. matt1e

    matt1e

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    Hi, more info req if you want a better answer PT44
    1) Post a picture of the wiring centre if you can, it will help
    2) how many zone valves do you have? post a piccy
    3) is the ufh controlled by a dedicated controller, does it also have a zone valve ?

    Matt
     
  6. picasso

    picasso

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    What controls your ufh ? do you have 2 port valves for the rads and actuators for the ufh or something different ? can you post pictures of the wiring and whatever controls you have.
     
  7. pt44

    pt44

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    No problem Matt - here is a picture of the u/f heating wiring centre side.

    The following images show the wiring centre and its diagram. It's wired exactly as shown. The connection to the boiler is as in Diagram 1 at the bottom. So it says to wire to N and s/l - unfortunately my boiler doesn't have s/l, it has Ns, Ls and LR. Hence my confusion ever since I installed it years ago. Worcester didn't want to help me, nor did Polyplumb.

    So the underfloor is only in one room and has its own thermostat, pump, two way valve, wiring centre etc. Then is has one wire going from the wiring centre to the boiler. This is currently connected to Ns and LR. Which kind of works - but not properly - as I cannot run the heating and u/f separately.

    Hope that makes sense.

    I should have added. The rads are supplied direct from the boiler. So it has its own internal pump etc. there are no other external valves on the circuit.


     
  8. matt1e

    matt1e

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    It does, your ufh is wired ok (well you dont actually need the N back to the boiler)
    S/L = LR btw

    and there is where your problem lies, you will need to add one to the rad circuit if you want to run the systems independently
    for now though it may be better to connect the new stat to control the boiler and disconnect the call for heat from the ufh controller
    that way the new stat would control the rads and the underfloor would still be controlled via its own stat (but still only when the rads are on)
    as said you will need to instal a valve if you want to do it right
    how is your hot water heated btw?

    Matt
     
  9. boilerdoktor

    boilerdoktor

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    you LS should be the supply of 240v out of boiler to external controls and LR is the switched live back.
     
  10. pt44

    pt44

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    So my u/f is wired correctly (I'm amazed).

    The water is all internal, it's a combi boiler. So the rad circuit is also internal, in the sense that it runs using the boilers own pump etc.

    You say I need to add one to the Rad circuit - add what exactly?

    When you say disconnect the call for heat on the ugh, what does that mean exactly - sorry, I'm not great with the correct terminology (half my problem of being an amateur who likes to tinker with his electrics). If you are saying that I need to add a valve to the rad circuit - I don't see exactly how that would help. Surely I just need the ufh to tell the boiler to fire up. Which, in my head is the same as adding a new thermostat, which also will tell the boiler to fire up (hopefully) i.e. they do the same thing, but when the ufh does it, then its valve also opens, flowing water round its circuit.
     
  11. matt1e

    matt1e

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    a separate zone valve, of course this may not be easy as it depends on your rad pipe layout with respect to your under floor manifold

    I mean disconnect the wiring to the boiler from the underfloor heating controller

    yes they will do the same thing but in your above reasoning you are forgetting that if the underfloor controller does it then the rads will also get hot and your new stat will be rendered inoperable as it will be overridden by the underfloor stat
    Is that the way you want it to work? then wire the new stat to Lr, Ls (and Ns if the neutral is req) and leave the connection from the underfloor heating in

    Matt
     
  12. pt44

    pt44

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    I can see your point Matt - to get my system running perfectly as 2 zones, I would need a second two way valve on the radiator side. I'd presumably place that just before the Flow pipe separates - where it T's and one pipe goes off to the UFH (which has its own 2 way valve) and the radiator flow goes to the rads.

    However - let me simplify my original question.

    If I totally ignore the UFH - pretend I don't have it for now. I have a Worcester Bosch 40Cdi with a wireless optismer and a slot in board on the front of the boiler, that controls water timings (eco setting of combi) and is also the stat receiver.

    Let's throw the wireless stat in the bin. Buy a new stat at B&Q. I now have to wire that stat to the boiler. I have two wires - its a simple switch after all. Which connections do I make?

    My presumption is one wire goes to Ns (Neutral Switched) and one wire goes to Ls (Live Switched).

    Is that correct?

    I want that one stat - to turn fire the boiler, on demand. Simple as that.

    Once I get that connection, then anything else is simply an external wiring centre surely, that fires the boiler as per the zone that requests it. At the moment, I don't have that, what I have is the inability to fire the boiler on request - it will only fire when the wireless stat tells it to.
     
  13. pt44

    pt44

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    I just found the installation instructions for the boiler. This is where the confusion has always been. The 40Cdi want you to have 3 wires from your thermostat/programmer.

    My underfloor heating exports two wires. Not three.

    I would have thought a thermostat normally only has two wires - it's a simple switch, either open or closed. But maybe I'm wrong.

    My thinking as a simple layman, is if I connect A+B then the boiler should fire up. I shouldn't need to connect A+B+C to do that. Therefore, I should be able to connect my N and s/l wires from my UFH to my existing boiler and when the UFH demands heating, the boiler should fire up. How I have it wired at the moment doesn't allow that.


    sure, this will mean that my ufh thermostat is controlling the whole house - I understand that. But I can solve that problem later on. At this moment in time, I simply want to get one wired stat to fire the boiler on demand.
     
  14. matt1e

    matt1e

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    your confusion arises because some 230v stats req a 3 wire connection to work efficiently
    there will be 2 for the switch part of the stat and the third provides a neutral for the anticipator
    the boilers two wire stat connection terminals are Ls and Lr
    do not connect a 2 wire stat to Ns & Ls under any circumstances
    Things will go bang :eek:

    Matt

    Ps heres a pic of what you need to know

     
  15. pt44

    pt44

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    So If I was connecting a two wire stat - I would use?

    Ls & LR?

    That's what I don't understand. In theory my underfloor heating control should put out two wires - they demand the boiler to turn on. But, they are listed as a Neutral and a s/l (I presume switched live). So, I connected them to Ns (neutral) and LR.

    I probably tried Ls at some point and got a nice bang :) Didn't do it again.
     
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