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Baxi Combi 105HE Central Heating Problem

Discussion in 'Plumbing and Central Heating' started by Tinkershole, 23 Oct 2018.

  1. Tinkershole

    Tinkershole

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    Good Morning All,


    I have a Baxi Combi 105HE.


    The boiler doesn't appear to be firing when the demand for Central Heating is set to occur.


    If I run a hot tap, the Central Heating LED goes out, the Hot Water LED illuminates and the boiler fires.

    When I close the tap, the Hot Water LED goes out, the Central Heating LED illuminates and any residual heat travels into the radiators (which I assume suggests that the diverter valve is working as it should).


    Could it be a sensor problem or a thermostat (or, even PCB)? Any suggestions how I might test with my meter?


    I'll post a photo of hot water running (whilst central heating should also be on).


    Should the Central Heating LED go out when a hot tap is run?


    Thanks in advance....
     

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  3. wingnut12

    wingnut12

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    Hi
    Did you ever get this fixed???
    The ch led SHOULD go out when you run you hw, have you checked the micro switches on your diverter valve The rear most on top is you CH, the front one is HW
     
  4. bazdaman

    bazdaman

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    The rear most on top is not a CH micro switch, it proves the pump is running and has to prove on HW and CH
     
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  5. ianmcd

    ianmcd

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    Wrong there is no CH micro switch
     
  6. Wilson78

    Wilson78

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    This is from October 2018! Anyway when ever someone says " the back microseitch is the central heating "
    Someone always says " no it isn't "
    At the end of the day it proves the pump etc and it's called the central heating differential valve , so I don't see any issue with it being called the ch diaphragm .
     
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  8. ianmcd

    ianmcd

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    Totally wrong, it is the pump proving switch, or primary flow switch it operates on both CH and DHW demand it tells the boiler that it has water and that the pump is running, never a CH diaphragm or CH micro switch
     
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  9. Tinkershole

    Tinkershole

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    PCB fault. Capacitor failed. After troubleshooting the guts, it could only be the PCB mis-firing - it recognised the demand for heating but didn't send the right volts to fire the heat exchanger.

    When hot water was being called for, the boiler fires up and hot water is produced. When switched to central heating, the boiler isn't firing up and any residual hot water, from when it had fired up under hot water demand, passes to the rads. Which tells me that the diverter valve is functioning as it should (I also tested to be sure it wasn't kicking in and out for some reason).

    With everything else functioning, it left only the PCB. £30 exchange at a local electronic shop found on ebay for a re-conditioned board with one year guarantee. Amazing.
     
    Last edited: 21 Jan 2019
  10. Wilson78

    Wilson78

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    Just a follow up, I'm not making arguments as it seems to have boiled your **** but....doesn't this give my comment any weight?! Just saying! It might not be ch diaphragm as we know it but.... I'll leave it there.
     

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  11. bazdaman

    bazdaman

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    That's not the boiler he is talking about, that is an instant
     
  12. Wilson78

    Wilson78

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  13. DIYnot Local

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