Help with Thermostat wiring, please!

Discussion in 'Plumbers' Talk' started by DickyRobbo, Nov 21, 2020.

  1. DickyRobbo

    DickyRobbo New Member

    Hi all,

    Really struggling wiring up some thermostats.

    I have a combi boiler. The thermostat I removed was wired in as below;

    [​IMG]

    A grey wire and exposed earth wire weren't connected.

    Here's the instructions.

    [​IMG]

    Now I tried connecting as the instructions say, the thermostat powers on etc but it does not kick the central heating on!

    Found a user who connected as my picture below, doing it that way for me provides no power to the thermostat and it doesn't turn on or do anything!

    [​IMG]
    Can anyone advise? What am I doing wrong? The only way the unit powers up is with brown in 1 and black in 2.
     
  2. Mike83

    Mike83 Screwfix Select

    Is the first picture your old thermostat?
    If so was it powered by batteries?
     
  3. DickyRobbo

    DickyRobbo New Member

    Yes, had batteries
     
  4. Mike83

    Mike83 Screwfix Select

    You’ll definitely need 3 wires maybe 4.
    It depends on what voltage the boiler is switching.
    Your grey wire may also not be connected at the other end.
    You need to trace this cable and check it.
     
  5. DickyRobbo

    DickyRobbo New Member

    Its a Logic Combi ES35 if that tells you anything. I'll have a look at the grey wire now.
     
  6. Muzungu

    Muzungu Screwfix Select

    You are assuming that brown is live, grey is neutral and black is trigger for the boiler and that the boiler is 240v switching. How have you made sure you know that?

    *Edit - Mike's on the case ignore me.
     
  7. DickyRobbo

    DickyRobbo New Member

    How can I establish this for sure? I have a voltmeter. I'm just about to access the boiler wires to confirm hopefully.
     
  8. Muzungu

    Muzungu Screwfix Select

    Boiler side first to see where they all go and if it's 240v switching, then work from there. You can now, however, measure the voltage between black and brown with the wires out of the unit but still trace where everything is going.

    I'll leave this for Mike to pick up on.
     
  9. Mike83

    Mike83 Screwfix Select

    If you can trace the cable then it can be installed just by identifying the wires.
    It’s probably just a matter of connecting the extra wire to a neutral but needs confirmed.
     
  10. DickyRobbo

    DickyRobbo New Member

    [​IMG] [​IMG]

    Does that help? First photo from manual second actual.
     
  11. Mike83

    Mike83 Screwfix Select

    The white cable that enters the boiler and the grey cable from the stat.
    Do these cables meet at a switch next to the boiler?
     
  12. Mike83

    Mike83 Screwfix Select

    The grey and black on the boiler are connected to the cable at your stat somewhere.
    You need to find this.
     
  13. DickyRobbo

    DickyRobbo New Member

    Yes I believe so....

    [​IMG]

    [​IMG]

    Theres 2 grey cables, 1 run upstairs the other for downstairs.
     
  14. Mike83

    Mike83 Screwfix Select

    The neutral (grey) on the stat cable look like it’s connected.
     
  15. DickyRobbo

    DickyRobbo New Member

    Ok. So what does that mean?

    Thanks so much for the help btw!
     
  16. Mike83

    Mike83 Screwfix Select

    BDCA5A01-2CA6-49E9-8042-6107C56C3F01.jpeg This earlier picture looked correct.
    If you disconnect the brown and black one of the wires should be 230v.
    This would be the live.
     
  17. DickyRobbo

    DickyRobbo New Member

    I only seem to get power to the stat (so the screen works) when the brown and black are in 3 and 4.
     
  18. Mike83

    Mike83 Screwfix Select

    We know that the brown and black are common and switched live. They turned the boiler on and off with the old stat.
    What we don’t know is what one was the common.
    With the old stat it didn’t matter what wire was in what terminal but it does now.
    It should be simple to wire from what you’ve exposed.
    You only need the 3 wires then a link from live-1 on the new stat.
     
  19. DickyRobbo

    DickyRobbo New Member

    I'm officially stuck then. Only ever get any power if black and brown are in 3+4.
    Tried to measure volatge but not sure my multimeter is correct. Brown is constant 24.5v, black is 0 and grey is constantly going up or down.

    Worth noting I've got 2 stats an both give same results.
     
  20. Mike83

    Mike83 Screwfix Select

    2 stats.
    That must mean you have zone valves then.
    Can you locate them and their wiring?
     

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