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Hive dual channel installation help

Discussion in 'Plumbing and Central Heating' started by Reece Laurence, 15 Sep 2019.

  1. Reece Laurence

    Reece Laurence

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    Hi,

    Hoping to get some help with how to wire a dual channel hive system on an old Worcester Danesmoor 20/25 boiler. Thought it was just going to be a simple swap as the old controller (external from the boiler) had what looked to be the same wiring setup as hive. But looking into it a little bit more I don't think it's ever been wired up correctly as the system isnt anything I've seen before.

    This boiler has 2 grundfos pumps, 1 for the hot water, and the other for the central heating. How the old controller works is that the hot water can be switched on which switches the boiler on. But if you want the heating on, the controller automatically turns the hot water on as well, looking at the controller wiring that is the only way how the heating will work as there is only 1 feed going to the hot water pump and nothing to the boiler.

    Is there any way that the 2 can be wired into the boiler separately so that the heating can be switched independently without the hot water having to be switched on as well ?

    Thanks in advance
     

    Attached Files:

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  3. Reece Laurence

    Reece Laurence

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    My thinking would be to wire it through the pumps and then to the boiler ? But following the diagram for the boiler I cant see how 16.B would fire up the boiler
     
  4. ericmark

    ericmark

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    Only way to use two pumps is with two relays, the relays act like non return valves. As if you connect supply to pump to boiler as well directly then both pumps will always run together. So controller feeds thermostat, and thermostat feeds pump and relay and the relay contacts turn on the boiler. With Hive no Thermostat for CH. But as said only if non return valves fitted as a pump not running will pass water in reverse direction as I found out.

    My radiators would heat up reverse direction to when pump running, not as hot, but still heated up. The plumber tested by turning off the isolator valves on the pump, and proved if you could stop water through pump then the radiators would stay cold. So he decided to fit two motorised valves, as each motorised valve has a micro switch built in, so pump and valve powered together and micro switch would power the boiler.

    I personally did not like this as pump is running before valve has opened, so not quite wired that way, I have one central heating system for the house as master, and flat central heating as slave so flat central heating will only work when house central heating is running.
     
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  5. stem

    stem

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    The problem you have, is that whilst both the heating and hot water have individual pumps, they both must operate the same boiler. So, it will have been wired such that the hot water side of things controls the hot water pump and the boiler, and the heating side just controls only the heating pump, hence why the hot water also has to be 'on' for the boiler to operate when heating is required.

    Usually fully pumped systems have just one pump with motorised valves to provide flow control to the heating and hot water as required. The valves have small switches built in to control the boiler and provide isolation between the heating and hot water control controls, as per below.

    mv.png

    As @ericmark mentions relays can be used to provide isolation. A relay wired to each pump will provide a voltage free contact that can be used to control the boiler and provide the isolation required between the two circuits.

    Drawing1 Model (1).jpg

    Alternatively, if you don't want to add relays, or motorised valves, you can replace the existing programmer with a Hive Dual channel version, and set it to 'gravity fed mode' this will replicate what you have now in that the hot water will be switched on automatically when the heating is required.
     
    Last edited: 16 Sep 2019
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  6. Reece Laurence

    Reece Laurence

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    Thanks both, I thought that would be the case having to fit relays. I may be looking at the actual wiring (not the diagram) wrong but I dont think it's ever been wired up correctly. As the feed to the boiler comes off of the hot water from the old controller external from the boiler ?

    Whereas looking at the diagram the boiler should have a constant feed to L N E and then the boiler is fired up from terminal 1 for HW and terminal 2 for CH, but looking at it I cant see how it would start the boiler up. Or am I looking at it wrong ? (See the attachments for diagrams on first post)

    @stem the hive system that I have got is a Dual channel one. How does the gravity fed mode work? Or how do I enable it I should say.
     
  7. ericmark

    ericmark

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    C-Plan_old.jpg This is C Plan without a motorised valve, there are a few versions of C Plan, note the cylinder thermostat needs both NO and NC contacts so three core and earth cable to it, with this system you can have hot water without central heating but not central heating without hot water, and because you can't turn off the hot water the boiler does not really need an over run. At least that's what my plumber has told me.

    With Hive 4 and 5 would be linked you don't need a room thermostat. I use Nest which has volt free contacts and no tank thermostat DHW is controlled in summer purely by time, but Hive will not allow that as there is no access to the com terminal of the DHW relay. However the way Hive connects to TRV's seems better.

    diagram2-old2.jpg This shows the plumbing, please note I am an electrician not a plumber, I wire up the systems I don't do plumbing. What I found was a problem was an enclosure for relays, likely the best idea is a mini consumer unit with din rail relays, but relays don't tend to have covers over their terminals as in the main designed to go inside some enclosure.
     
  8. stem

    stem

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    If I understand you correctly, in that you mean that the boiler is wired to the 'hot water on' control, then that is the correct way of wiring it for your installation. As I explained before....
    From the Hive manual:

    Capture.JPG

    Yours isn't actually by definition 'gravity fed' but will have been wired up as such to get over the boiler control switching issue.
     
    Last edited: 16 Sep 2019
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