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Thread: Evohome set to off but boiler fired up minutes later.

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    Automated Home Sr Member
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    Default Evohome set to off but boiler fired up minutes later.

    Are there any reasons why after setting the heating to off the boiler minutes later would fire up? I don't just mean the pump overrun I mean flame on. The boiler showed heating on rather than the expected "Ready"

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    Automated Home Legend paulockenden's Avatar
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    When you set the heating to off the low temp is passed to the HR92s (or whatever) sometime over the next five minutes. They then screw their valves down, then report back zero heat demand to the controller. Only when all zones are reporting zero will the controller tell the boiler relay to stop demanding heat.

    In other words, it can take a few minutes - even longer if a transmission gets lost.

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    Okay thanks only ideal were replacing a thermostor and with the heating turned it fired up a good few minutes later. I thought as much, sure I've had it before where I've set a new zone temp and that's took a while, not always instant.

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    If you're doing plumbing work on the heating system that requires the boiler and pump to definitely stay off I would not trust the Evohome system's built in Heating off or Away actions to do this.

    As explained there is a long sequence of events and wireless communication involved from you choosing the quick action until it is finally actioned, and it can in some circumstances not happen as expected, and at the very least will take a few minutes. If you're unlucky with the timing of the TPI cycle it may even appear to come back on after you have turned it "off", at least for a few minutes.

    Not to mention that someone could manually turn up an HR92 in any room while the system is being worked on and cause the boiler to be fired again even though the controller reports Off.

    Always isolate the mains supply to the boiler/pump/BDR91 etc before carrying out any electrical or plumbing work on the system. I'm surprised that your plumber did not do this. I have a fused switch beside my main BDR91 which cuts all the power to the whole heating system before the wiring centre, I use this before I do any plumbing work on the system to ensure the boiler and pump cannot start unexpectedly, and if I do any electrical work on it I also isolate it at the main consumer unit as well as at the fused switch for added safety.
    Last edited by DBMandrake; 11th December 2017 at 10:07 PM.

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    Automated Home Ninja Dan_Robinson's Avatar
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    Quote Originally Posted by DBMandrake View Post

    Always isolate the mains supply to the boiler/pump/BDR91 etc before carrying out any electrical or plumbing work on the system. I'm surprised that your plumber did not do this.
    Gotta love the irony of this advise given the fact that you DIY'ers are poking and prodding around in boilers that require certain checks when the covers are removed that you're not equipped to perform (Vaillant owners in particular ).
    Kind Regards - Dan Robinson (Jennings Heating Ltd)

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    Just to point out of was after the Thermistor was changed, which in my boiler only clips onto the pipe anyway.
    He was watching the flow and return temps then switched it off to see the pump overrun it then went off, but came back on which stumped him.

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    Quote Originally Posted by Dan_Robinson View Post
    Gotta love the irony of this advise given the fact that you DIY'ers are poking and prodding around in boilers that require certain checks when the covers are removed that you're not equipped to perform (Vaillant owners in particular ).
    How is it ironic ? I don't touch anything gas related on my boiler, that includes gas pipes/fittings, nor have I ever opened the seals on the fire box. What checks in particular are you referring to ? Since you don't even know what kind of boiler I have I suspect you're jumping to conclusions here...

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    Automated Home Legend paulockenden's Avatar
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    Quote Originally Posted by dan_robinson View Post
    gotta love the irony of this advise given the fact that you diy'ers are poking and prodding around in boilers that require certain checks when the covers are removed that you're not equipped to perform (vaillant owners in particular ).
    MRDA. ;-)

    p.
    Last edited by paulockenden; 12th December 2017 at 01:08 AM.

  9. #9
    Automated Home Ninja Dan_Robinson's Avatar
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    I suspect that arguing from a point of ignorance is a tad silly.

    Just because YOU don't see what is needed does not mean it doesn't exist.

    I know not, and care less what boiler you have DBM - I was replying, lightheartedly, to a general bit of advise about turning power off before working on a system (which is rubbish advise anyway as most checks on a modern boiler require live testing).
    Kind Regards - Dan Robinson (Jennings Heating Ltd)

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    Quote Originally Posted by Dan_Robinson View Post
    I suspect that arguing from a point of ignorance is a tad silly.

    Just because YOU don't see what is needed does not mean it doesn't exist.
    Stooping to name calling and making claims of ignorance is not doing your argument any favour. It would behoove you not to make assumptions about what individual DIY'ers do or do not know about anything, and what they are capable of.
    I know not, and care less what boiler you have DBM
    Of course it matters. You're implying that "we" are routinely touching things that we shouldn't be, so I've asked you to provide a specific example of what your concerns are rather than a hand wavy "oh its too scary and dangerous, don't touch it, only us experts know what we're doing" assertions.

    You're trying to imply even removing the covers on boilers needs gas safe training - nonsense. My boiler has a user removable cover (without screws) that exposes all the gubbins with exposed gas pipes, gas control unit, mains wiring, the whole lot all just sitting there in plain view - you have to take the front cover off and expose all this just to adjust the thermostat or light it!

    I'm sure there are boiler designs where you can't get at some of the non gas stuff (plumbing, temperature sensors, PCB etc) without disturbing the gas pipes, gas control unit etc - in that case fair do's. But that is on a boiler by boiler basis, and depends on what exactly you're trying to get at in the unit.
    - I was replying, lightheartedly, to a general bit of advise about turning power off before working on a system (which is rubbish advise anyway as most checks on a modern boiler require live testing).
    So turning off the power before working on a system is bad advice ? Ok.... I'll file that piece of advice away in my waste paper bin...

    I misread the original posters post - I thought they were breaking into the plumbing side of the system without ensuring the system was properly off - and as pointed out, Evohome has a much broader and greyer definition of "Off" than most standard control systems, so my advice was to make sure the system was really turned off at the mains before cracking open any plumbing, least the Evohome surprise you by turning the boiler back on and pumping water everywhere... I think this is a perfectly legitimate piece of advice when most people don't realise what "Off" really means on an Evohome.

    And it should also be turned off before working on any of the electrical wiring, including changing a thermistor - anyone changing something like that without turning the power off isn't as qualified as they think they are.

    Of course "checks" will require the power to be on again after the work is done. Duh.... so I'm not even sure why you mention that.

    Carry on...
    Last edited by DBMandrake; 12th December 2017 at 02:05 PM.

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