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Drayton Wiser Heat Hub wiring

Discussion in 'Electrics UK' started by plumbamateur, 7 Feb 2021.

  1. plumbamateur

    plumbamateur

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    I'd appreciate some advice with wiring for a Drayton Wiser Heat Hub.

    I have a Vaillant ecoTec 837 combination boiler, currently controller by a Honeywell programmer in the hallway. On removing the Honeywell controller, it appears it's connected to the boiler with only 2 wires (a permanent live and a switched live).

    I believe I will therefore need to provide a separate 230v supply to the Wiser Heat Hub. I have an existing 3A fused spur ajacent which I plan to use for this purpose.

    I'm confused with the wiring requirements on the new Wiser backplate. I have purchased the 2 channel version of Wiser (which includes HW control, which I don't currently need). So I need to use the 2-channel Heat Hub as a single channel unit, simply to control the Vaillant combi for heating only.

    I will have 4 wires available at the backplate (live+ switched live to the boiler), plus L and N from the new 240v supply. I'd be grateful for some guidance as to how to wire this, the Drayton wiring diagrams don't cover my particular scenario in using the 2 channel unit for 1 channel operation!

    Many thanks in advance
     
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  3. stem

    stem

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    The Two Channel Wiser wiring connections are:

    Capture.JPG

    You are right about the power supply to N and L, That should be come via the same 3A fused spur that supplies the boiler.

    The central heating 'ON' terminal of the Wiser is (4) The 'switched live' removed from the existing programmable thermostat goes in here.

    The permanent live that presently goes to the programmable thermostat isn't required so can simply be insulated / isolated safely out of the way. Or, because both 'lives' are via the same fused spur, it can be parked in the (L) terminal with the new live you will be installing.

    Wiser has the live connection link made for you already internally. Shown in brown below, so the additional live wire from the thermostat is not required:

    Capture1.jpg

    Important note: When you say:
    I have assumed that this is correct and that you have confirmed it, and not just assumed it. Some boilers are wired with 24V control direct from their internal circuit boards. If this were the case, if you were to put 230V on a 24V circuit board the results would not be good.

    If you wanted to use Wiser with 24V boiler control, you would need the One Channel Version.

    Capture2.JPG

    As you can see here, the internal link to the live is not present, and instead a COM terminal is provided. The 24V connections are made to COM and ON which are isolated from the 230V supply.
     
    Last edited: 7 Feb 2021
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  4. ericmark

    ericmark

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    With any thermostat first job is look at the boiler installation instructions.
    temp.jpg
    This seems to show three options ebus, 24 volt, or 230 volt so you need to find out which you are using, with a single channel with standard back plate on/off then you can have an independent supply for thermostat and boiler, however since the same back plate can be used with single, duel, or three channel in interests of safety should use same circuit as boiler if possible. I personally think using the same back plate for volt free and low voltage (230 volt) is flawed, it is too easy to fit wrong thermostat.

    It is a historic thing same back plate was used for programmer and thermostat, but you were unlikely to put a programmer on a thermostats back plate. Hive does the same.

    Theory is a circuit is an assembly of electrical equipment supplied from the same origin and protected against over current by the same protective device(s). So if there is a fuse in the boiler, to be on the same circuit it would need to come from that fuse, but it is normally considered if from the same fused connection unit that is good enough. Many boilers state the boiler and controls should be from same supply, I would assume they mean circuit as most homes only have one supply.

    However since this boiler says unless fitted where plug and socket are not permitted it should be supplied by a 13A plug and an switched socket and plugs designed for two leads are rare, you need to do the risk assessment.

    Personally if cover can be removed without disturbing gas tight seals I would supply from boiler, other wise would use a switched FCU with two cables coming out. With a two pole switch. If possible lockable.

    But @stem has beat me to it, first you need to work out if using 24 volt or 230 volt. The Drayton Wiser comes in 4 versions, single channel, duel channel, three channel and opentherm, the latter would be the best. And with the latter it seems OpenTherm comes from the OpenTherm module not connected to back plate. temp2.jpg Since my boiler does not have option I have not looked into OpenTherm that much.
     
  5. CBW

    CBW

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    Depending on how old your combi is, depends on the Voltage output for room thermostat, if it’s the 2006 - 2010 model, I’d suspect 230vac live out and return, but as per @stem and @ericmark , this needs confirming. Personally I’d be taking 5 core heat resistant flex from under the boiler to the receiver, and disconnect the old wiring.
     
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  6. stem

    stem

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    Hi @plumbamateur. Just wondering how you got on? As we have responded to your request for assistance, it would be nice to get some feedback. It may also help others that come across this thread when they are searching for help to install their Wiser.
     
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  7. plumbamateur

    plumbamateur

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    Hi @stem - firstly - apologies for not responding. I had to leave it last weekend as a) i'm so busy in the week, and b) it started snowing so I decided not to start mucking about with the heating :)

    Secondly - thank you SO much for the comments above. Really super-helpful. The Drayton wiring diagram isn't 100% clear on this - but your diagram with the brown connection above makes complete sense. Luckily, the 3A fused spur I was planning to use is indeed the exsting one which supplies the boiler. [Incidentally, on checking this, it had a 13A fuse fitted - now corrected - this must have been in place for ~10 years since the boiler was fitted!]

    Thank you also for your advice regarding 240v v 24v wiring to the old thermostat/controller. Bsaed on your comment, I tested the L using a multimeter to earth, and it is indeed @ 240v - so your guidance was correct. Parking the existing L from the boiler in the same terminal as the new L supply now makes sense - thanks.

    @ericmark thank you for your comments. No OpenTherm unfortunately on the Vaillant - I guess it's not modern enough. I decided, based on confirming the 2-wire 240v Live/switched live setup that I'd leave investigating at the board in the boiler, and leave the cover happily in place :)

    Thanks once again to all for the assistance, and the time you invested pasting diagrams etc. I'm really most grateful.

    enjoy the weekend,
    Plumbamateur
     
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  8. ericmark

    ericmark

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    I am undecided as to advantage of OpenTherm, but does not really affect me with an oil boiler, over shooting however is a problem, my hall is too slow to cool, so if it over shoots, all other rooms get too cool before the boiler comes on again.

    Hind sight is easy, I realise Nest Gen 3 was not the right option for my house, and the Drayton Wiser would have been better, but the temperature variation across a rooms is not something I have had before, the Myson fan assisted did ensure even heating throughout the room.

    The modulating boiler my mother had resulted in radiator temperature varying gradually, but here not convinced the programmable TRV heads help as the boiler turns on/off not up/down like mothers. However reading the spec it does seem the Drayton Wiser TRV heads are best on the market, so would love to know how it all works out.
     
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