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Replacing analogue with digital room thermostat

Discussion in 'Electrics UK' started by Canon, 17 May 2012.

  1. Canon

    Canon

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    Hi
    I know this question has been asked before on this forum but I am still uncertain of what to do. I am replacing an old analgue room thermostat with a Syxthsense SST-A230-304 digital one http://www.syxthsense.com/product/product_pdf/TH6.90-STT.pdf

    Having taken off the old thermostat I have 3 wires, red, yellow and blue which i have assumed relate to live, heat and neutral.

    Here's the wiring diagram for the new thermostat:


    I have connected the red wire to live, the blue to Neutral (The N closest to the corner of the unit) and left the Yellow free but it is not working. Can anyone tell me what I have done wrong and if I am likely to have damaged the new unit?
    Many thanks
     
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  3. Taylortwocities

    Taylortwocities

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  4. Canon

    Canon

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    Many thanks for the Hint, I had seen that post but still not bright enough to figure this out I'm afraid. I have now got Yellow to Load, Blue to Neutral and Red to live but the unit will not power up :( It might be time for me to pay a professional.
     
  5. ericmark

    ericmark

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    This type of thermostat is for underfloor heating and has separate sensors one in floor and one in the room.

    I have used a cheaper version where the room sensor is built in to the thermostat and that type will work without the underfloor one being connected.

    Are you using this for under floor heating?
     
  6. ericmark

    ericmark

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    The link only covers normal central heating this post is for a underfloor thermostat which has two separate sensors which need connecting to measure the room and floor temperature.

    The link he gives does detail how it is to be connected and one would have at least 5 wires. He only has three.

    A quick read does talk about advanced parameters and how they can be set. It is parameter 3 from what I can see which allows internal or external sensors to be selected.

    But its not a standard thermostat and I wonder if he really needs such a complicated device? Main point is it has 16A contacts.
     
  7. matt1e

    matt1e

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    Not the model that he has, it should be fine
    is there any display at all? are you sure that the thermostat wiring is switching 230vac,as it may be voltfree now on old wiring

    more info req on boler and system

    Matt
     
  8. Canon

    Canon

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    Hi, I'm not using an underfloor sensor (yet) and at the moment there is no display or life to the unit at all, so I'm not able to reconfigure the advanced parameters. I hope I haven't blown it up by wiring it up wrong the first time - is there a way I can check?
    I can't confirm the wiring is switching 230vac, the old thermostat is a Satchwell Type TL if that sheds any light - its probably over 20 years old as I have just replaced an old Potterton floor standing boiler (with a glow worm Ultracom 30hxi) that I assume would have been put in at the same time.
     
  9. EFLImpudence

    EFLImpudence

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    Perhaps that's where the fault lies.

    Wire the thermostat to a plug and see if the display works.
     
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    Taylortwocities

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    Or put the old stat back (hoping you noted where the wires went?)
     
  12. Canon

    Canon

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    Old stat is back and working.
    Have just wired new one into a plug and it works (hooray & phew), see photos:




    Would it be worth me buying a meter to see what is happening at the red and blue wires coming out of the wall?

    Really appreciate your continued advice.
     
  13. ericmark

    ericmark

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    I will guess you have no neutral. With most of the old thermostats the neutral was used to reduce the difference between on and off temperature but not connecting the neutral would not stop it from working.

    As to buying a meter I was surprised to see in a class of around 16 'A' level physics students how half of them managed to blow the fuses in the meter when set what to me seemed a very simple task. So I would not recommend buying a meter I would say getting an electrician to do it for you likely more cost effective.
     
  14. EFLImpudence

    EFLImpudence

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    Can you see/determine where the other end of the R/B/Y wires go?

    What make and model is the boiler?
     
  15. Canon

    Canon

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    Instead of buying (and blowing the fuse on) a meter I have used a 60W bulb; neither combination of red and blue, or yellow and blue wires light the lamp. How the existing thermostat works is a new mystery. I will seek professional help, thanks to all of you who have responded.
     
  16. Canon

    Canon

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    Its a glow worm Ultracom 30hxi boiler. I can't directly trace the wires, they disappear into a concrete wall in the hall, I assume head vertically up to cross and come back down into the utility room where the boiler sits. Taking the cover off the power unit to the boiler I can't determine if the cables emerge here or not; here is what i can see:

    Boiler power unit inside of cover:


    Boiler wiring:

     
  17. Taylortwocities

    Taylortwocities

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    The room stat is on 2 and 3 according to the box. But it may not be wired up excatly like that.


    The yellow wire on 2. See if you can see the cable that it comes from and come back and tell us where the red and blue wires from that cable go to.
     
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