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Nest Installation with unvented Hot water tank

Discussion in 'Electrics UK' started by aky20, 19 Jan 2018.

  1. aky20

    aky20

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    Hi there,

    I am seeking some assistance to determine if it is possible to connect a Nest thermostat to a Megaflo 125DD which currently has a Horstmann Electronic 7 Digital Economy 7 Timer & Boost Control currently fitted.

    I have been in touch with Nest who confirm compatibility, however when I have spoke to Nest installers they seem to be clueless.

    The hot water thank is operated of the mains electric, so cannot see a reason why it wouldn't work. I know the unit will not control my heating as I have electric heaters which have an independent timer and thermostat.

    With Nest I think I will lose the boost function, but it is pretty rubbish in that only one element comes on to provide additional hot water as needed.

    With Nest I should be able to set up my own schedule according to my own requirements.

    Thank you in advance for your help.

    Cheers
    Aky
     
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  3. ban-all-sheds

    ban-all-sheds

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    Seems like a madly expensive and complicated way to provide a timer for an immersion heater.
     
  4. aky20

    aky20

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    Just been told by someone else that my system is not compatible and to make it work, it would need a rewire and a powerful switch installing.

    Can anyone shed any light on what the plumber is referring to?
     
  5. aky20

    aky20

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    It is, but the timer is rubbish and we are forever running out of hot water and it is a pain to go and press the boost button to get some more hot water.
     
  6. Taylortwocities

    Taylortwocities

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    Yes. You are planning to use the NEST to switch the immersion on and off. That needs nearly 13amps. The NEST contacts are only good for 5amps at best. So, for starters it will not work.
    Secondly, lets say its christmas and you've run out of hot water, how are you going to boost it?

    Also you MUST learn about your E7 and how it works. The Horstmann is made to synchronise its times of operation to match the E7 times, and to provide the boost function. Really, leave that in place. Return the NEST for a refund.
     
  7. aky20

    aky20

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    I get that it is designed to run on the off peak tariff, but I could ensure I follow that within Nest.

    Also for the boost function, if it is anything Hive then I should be able to set the thing to run from the app as needed.

    Alternatively are there any better thermostats available that support smart functionality?
     
  8. Taylortwocities

    Taylortwocities

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  9. ban-all-sheds

    ban-all-sheds

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    What's a learning thermostat for heating systems going to learn if all it does is turn an immersion heater (whose thermostat it does not control) on and off according to E7 times, and now and then respond to a phone telling it to "turn on now"?

    Are you sure you aren't using a sledgehammer to crack the nut of an improperly set up E7 timer controller, or a faulty hot water cylinder?
     
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  11. AnotherTom

    AnotherTom

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    At the moment, your horstman probably controls two outputs, one for the off peak that heats the whole tank using the bottom element, and one for the boost that heats the top part only. It's done this way to save money - heating the whole tank with daytime electricity is expensive, but it also saves time because you can heat the top quicker than the whole tank. The standard Nest won't directly support this - it will be all or nothing, because it only has one output.

    If you would like the boost to heat the whole tank, you can modify the horstman's wiring to do that, but it may take more than one boost cycle to get properly hot, depending on the size and starting temperature of the tank.

    If you are keen to install the Nest, it could be wired through a contactor to control both elements together. Alternately, you could wire the nest (& contactor) to the boost element and keep the bottom element on a timer. If you want full digital control of both elements, you would need two Nests, or it might be possible with the 3rd generation heatlink unit, connecting one element to the heating output and one to the hot water output, but I'm not sure (contactors still required)

    HOWEVER: another very important function the horstman provides is to make sure only one element is on at once. If whatever modification you make allows them both to be turned on simultaneously, you may need to upgrade the supply from the consumer unit or else risk the system tripping out or blowing fuses.

    In this application (if you are using the nest as an internet connected switch, not as an actual thermostat) you could substitute any home automation type switch that supports your preferred app or IFTTT function, which may be cheaper.

    Altenative solutions might include:
    switching from economy 7 to economy 10, (and reprogramming the horstman accordingly) - this would give you some off peak electricity in the middle of the day
    a bigger cylinder
    reducing hot water consumption by fitting flow restrictors or low flow heads to showers etc.
    increasing the cylinder temperature (on the bottom thermostat) so that a given activity consumes less hot water and more cold
    making sure the bottom element actually works.
     
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  12. ericmark

    ericmark

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    I use Enrgenie MiHome but think there are other makes which do not need a hub so will work out cheaper. I can only tell you what the MiHome stuff will do, there are 5 options from a relay to a socket either mounted in wall or free or plug in. So does not matter which you have three timers, upto three remote controls, and can be used with phone, tablets, or PC.

    So you can set to come on during the 7 hours of low cost, and also two other times or use remote, What I do for the alarm that I use is have two times that switch off and on so if I switch it off it truns back on three times a day, you would want the reverse.
     
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  13. flameport

    flameport

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    Possible - yes, but then most things are.

    A sensible thing to do - certainly not.

    The lack of hot water requires further investigation, just shoving a totally inappropriate controller on there will achieve nothing.
     
  14. ericmark

    ericmark

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    I don't really like plugs and fuses for immersion heaters, as taking max output for so long, however a simple device like this smart adaptor would likely do what you want, I would look for an European version with no fuse, as a fuse means heat.
     
  15. Taylortwocities

    Taylortwocities

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    Only rated at 1800watts. Next?
     
  16. ban-all-sheds

    ban-all-sheds

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    upload_2018-1-20_8-48-21.png

    o_O
     
  17. Taylortwocities

    Taylortwocities

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    I read that from the FAQ for that product on the Maplins web site. Probably BAS’s info is correct.
     
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