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CH comes on even when boiler is set to HW only?

Discussion in 'Plumbing and Central Heating' started by xpeterpx, 23 Oct 2019.

  1. xpeterpx

    xpeterpx

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    Hi all
    Hope someone can help.
    Our CH comes on randomly even though the boiler is set to hot water only.
    Its run by a wireless Danfoss electronic timer - could this be activating the CH to come on even though the boiler is not set for CH to come on?

    Its an Ideal C30 boiler if that helps

    Thanks for any advice
    Pete
     
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  3. ScottishGasMan

    ScottishGasMan

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    If you have the control on the front of the boiler set to Hot water only then the external timer can not override this so even if timer was faulty and asking for heating the boiler will ignore it when on DHW only mode.

    As far as I know thats a combi boiler, and the probability is that the diverter valve may be failing and letting hot water pass into the heating by mistake, youd need a heating engineer to repair that.

    You could test it though, facing the boiler the Left hand most pipe coming down from the boiler should be the heating flow pipe, get a feel at it, then start running a hot water tap, if then the heating pipe starts to heat up then its almost cetainly the diverter valve.
     
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  4. xpeterpx

    xpeterpx

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    Thank you so much for your help.
    Diverter valve sounds about right. Will monitor it when the hot water is next on and post back

    Thanks
     
  5. oilboffin

    oilboffin

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    If it's a grant it could be a non return valve sticking
     
  6. ianmcd

    ianmcd

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    It is an Ideal C30
     
  7. xpeterpx

    xpeterpx

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    Quick update guys the diverter valve theory may be out as that heating pipe does not heat up when the hot water was turned on.
    The heating came in again in the night when no hot water was being used and the boiler is on hot water ONLY.
    Any other ideas what can at fault please?

    Thanks
     
  8. ianmcd

    ianmcd

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    When the boiler comes on when it is not supposed to what does the display show
     
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  10. xpeterpx

    xpeterpx

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    Will have to wait until it happens again. If there is an actual temperature display what are your thoughts?
    Or are you thinking along lines of a fault code?

    Thanks
     
  11. ianmcd

    ianmcd

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    Unlikely you would get a fault code if the boiler is actually running, you you should get a status code saying what demand there is, i.e. CH demand , HW demand, frost protection demand, pump over run,HW pre heat, if you let us know the status code we will be able to help you better
     
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  12. xpeterpx

    xpeterpx

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    Hi. Ok so noted the display.
    Just revisiting for more help please.
    Status is hot water & CH/ pre heat off.
    Just switched CH on using the wireless timer and the CH comes on nicley even though the setting is for HW only.

    Can upload a couple pics from my phone if I can just find out how to..
     
    Last edited: 3 Nov 2019
  13. ianmcd

    ianmcd

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    To upload a photo you click on upload a file, if as you say when the boiler is selected to HW only but you can over ride this by turning the thermostat up, then it is not wired correctly, @shambolic might know what could be wired wrong,
     
  14. stem

    stem

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    Do you have a frost stat thermostat fitted anywhere? They are usually wired to override the normal controls and turn on the heating to prevent freezing. Although, it would be unusual in this weather for it to get cold enough to trigger one though, unless it's inadvertently been set too high.

    Regarding the normal operating controls:

    The boiler has two external thermostat / timer wiring terminals, a 'Live' and a 'Switched Live'. When they are electrically connected the heating operates, when they aren't connected it doesn't. Simples!

    It's possible that it has been wired so that the 'Switched Live' fed back to the boiler comes from another live source (e.g. such as a mains powered thermostat receiver) instead of from the live terminal specifically supplied for the thermostat at the boiler. This is sometimes done to reduce the number of individual wires that need to be installed. Then, if the selector switch on the boiler is wired into the boiler's live thermostat supply it would turn it off when set to hot water only. However if the live came from an external source it wouldn't.

    Unfortunately, I don't know how the boiler is wired internally so the theory can't be confirmed without checking / testing the wiring. And whilst this theory might explain why the heating comes on when it's set to hot water only, it still doesn't explain why it's coming on randomly.

    I also seem to remember that the wiring terminals for this model are inside a room sealed part of the boiler. If so, accessing them is only a job for an RGI (Gas Safe) so that they can carry out the necessary safety checks to make sure the compartment is properly sealed up again afterwards.
     
  15. shambolic

    shambolic

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    Pcb gubbed. I’ve had it where people don’t know how to work programmer so keep turning summer/winter/off switch and it causing potentiometer to go a bit slack so you think it’s in hw only but it’s not. that switch is for occasional use ie once at start of summer and once at start of winter, not for turning on and off several times a day every day.
     
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