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Hive dual channel wiring help

Discussion in 'Plumbing and Central Heating' started by onlytim, 3 Sep 2018.

  1. onlytim

    onlytim

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    Hi I’ve bought a Hive dual channel with separate hot water tank system and am struggling with wiring for the hot water, the heating is fine. I have a Danfoss FP975 controller with wall mounted Danfoss thermostat, the controller is wired as below
    8931E5E8-F9C7-43D1-914F-1C67B0B1082A.jpeg

    I have wired the Hive as below, the heating works fine but I have got something wrong with the hot water side. If somebody can give me some pointers it would be much appreciated


    BF8EE1CC-4FD8-44D5-88FE-2CCE0028E417.jpeg

    Thanks in advance
     
  2. stem

    stem

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    First of all there was something odd with your original photograph. On page 9 of the Danfoss FP 975 Installation manual, it shows the terminal connections below. Terminal 4, is the output to put the central heating 'on'

    FP975.JPG

    However your photo doesn't have a wire connected to it.

    Existing.jpeg

    Instead you have a wire connected to central heating 'off' terminal 6, which very few systems require and even if your system was one of the very few that did utilise it, there would still need to be a wire connected to 4. So it wouldn't have worked like that. However, you say that the heating is working now.

    Regarding the control wires for the Hot Water at the FP 975. In your top photo, they are shown as the green/yellow (an earth wire being used as a live) and the red wire. At the Hive you are using a black wire and a red wire. So no idea what you have done there.

    If, and only if, the original programmer was installed properly and working properly, the wires would be exchanged as below:

    The wire that was in FP975 terminal 1 DHW on = Hive 3 Hot water on

    The wire that was in FP975 terminal 3 DHW off = Hive 1 Hot water off
     
    Last edited: 4 Sep 2018
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  4. onlytim

    onlytim

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    Hi Stem, thanks for the reply and help. The FP975 picture above is how I found it when I took the Controller off. I did notice the green/yellow wire going to terminal 1 and the missing wire for terminal 4 which didn’t add up to me. Is it possible there has been some sort of bypass using the terminal block in the middle or would you expect this?
    I had the Hive up and running and the heating worked fine, I will follow your advice on my next attempt and hopefully the HW will follow suit. My only question now is what happens to the black wire? Is it possible the wiring is wrong at the other end and that in fact is now the earth?
     
  5. stem

    stem

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    Unfortunately it is impossible to know with heating systems what each wire does according to colour. This is because the original choice of wire colour depends upon the personal preferences of the whoever installed it, and the cables they had to hand. Someone may choose to use a red wire for the Hot water 'on' someone else may choose to use a black wire, and someone else (who is not a follower of good practice) a green/yellow wire.:rolleyes: Also, as you suspect, it is quite possible that a wire changes colour en-route as it passes through a terminal block or junction box.

    If it had been wired correctly originally, the terminals to which each wire are connected would allow the identification of each wires function, which is why I said.

    When this is in doubt, the only way to know what each wire actually does is to trace it, either physically or with electrical test equipment and find out what is connected to the other end.

    In your photograph, the green/yellow wire in question, is connected to a terminal that the programmer makes live (terminal 1), so it is most certainly not being used as an earth connection.

    I did once come across a system wired like yours (many years ago) where a really old mechanical timer had broken, but it had been discovered that the heating 'off' function still worked, so they moved the heating 'on' wire into heating 'off' and set the programmer for the times that they didn't want the heating on. There are all sorts of other fudges that I have come across, but it would be impossible for the heating to have worked correctly as it was originally wired without a modification somewhere, for example a relay being switched by the heating off signal, or you had a programmable room thermostat that was controlling the heating on/off times instead of the FP975. Unfortunately, this may be an installation where you need to get a pro to physically come and sort it out for you.

    If everything was working correctly as as it should before you started, normally these exchanges are made by identifying the function of each terminal of the FP975 from the connection diagram and then the wires are moved across to the Hive terminals that are identified as having the same function. As you have figured, the brown wire links aren't required as the Hive has these connections already made internally.

    Because of the more important issues you have raised, I haven't asked about any existing room thermostat. If there is one, it needs to be taken out of operation as it can interfere with the operation of the Hive. It needs decommissioning properly though (or simply set to its maximum setting). It can't be just disconnected as the wiring will be left 'open circuit' and the heating won't work.
     
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