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2 x central heating boilers wiring ??

Discussion in 'Plumbing and Central Heating' started by Maciek, 24 Jan 2019.

  1. AGAS

    AGAS

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    RTFM ;)
     
  2. Maciek

    Maciek

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    I did. Posted a picture of it. tells me nothing

    If you don't like helping people for free I will pay you. Just tell me how to wire it.
     
  3. oilhead

    oilhead

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    You may wish to consider isolating the boiler that is not being used, otherwise a significant amount of the energy used will be heating a boiler for no benefit.
     
  4. bernardgreen

    bernardgreen

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    The instruction / installation manual should have far more information than can be shown in a single picture.

    The best help is being helped to understand the system you are hoping to install as a DIY project. That will be of benefit when it comes to fault finding now or later.

    Being told which wire goes where doesn't provide any understanding of the system. Giving "this goes there" instructions via back and forth typed messages and the advisor not able to see the equipment can result in a disaster.
     
  5. stem

    stem

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    This isn't simple. I agree with the others that it's not really safe to give advice on how to wire it up over a forum, but I'll quantify that.

    The first problem I can see is that the connection for the electric boiler thermostat is marked "voltage free" and "0V!!!" The present system you have with motorised valves is an S-Plan and they are not generally voltage free. It could be reconfigured so that the motorised valves do provide voltage free boiler control, but as you are wanting to keep the 230V controlled oil boiler as well then you have a bigger problem as you will want to use '230V' and 'voltage free' control. Not insurmountable for an electrical engineer or someone with a high level of electrical knowledge / understanding to get around, but will require additional equipment but it's not certainly not straightforward.

    The second issue is that you state that your boiler is a "Grant vortex eco external system" Now, I admit to not being familiar with this type of boiler, but according to a diagram below that I found in a copy of a Grant Vortex Eco manual on line, the pump in the 'system' model version is wired to the boiler and controlled directly by it. So, if the oil boiler is out of use, then you need to consider how to control the pump when using the electric boiler. Again not straightforward.

    grant.JPG

    According to the same manual 'System Models' also have an integral expansion vessel.

    System model.JPG

    However, previously you said "Both boilers will be open vented and fed from the tank in the loft" in which case it isn't a 'System Model' and the pump may be wired so that it's not controlled by the boiler. That may make it a bit easier but you will still have the 'voltage free' and 230V control issue.

    Other things to consider. The current heating system will likely be supplied by a 13A fused spur (fitted with a 3A or 5A fuse) the electric boiler will require a much larger electrical supply.
     
    Last edited: 19 Jun 2019
  6. Maciek

    Maciek

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    Ok. Thanks for some info.

    Both boilers are plumbed in the way so they can be shut off by valves so not being heated unnecessarily. Oil boiler can run in the loop in the winter if temp goes below 5C as being fitted outside the house.

    Electric boiler is connected to 63a rcd by 10mm^2 cable.

    I know how to plumb it or give correct electric supply. Its all been done already.
    I just dont know how to wire the controls with one thermostat and switch between 2 boilers, like a on off light switch.

    Looks like I have to put second control system, unless someone have other ideas. I can send more pictures.
     
  7. Maciek

    Maciek

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    I all fairness my plan was to take a wires from hive and connect them to 2 way light switch. Then one switch can operate oil boiler and other electric boiler.

    No issues with oil as it is already wired but issue with electric is that I still need a signal to put a pump and motorized valves on.
     
  8. ianmcd

    ianmcd

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    does your electric boiler not have two separate circuits ? should have the 63A one that you mention but should have a separate fused 3 Amp one for the controls side
     
  9. stem

    stem

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    You really are over simplifying it.

    Let's start with the real basics. When you propose:
    That is completely wrong, it's the motorised valves that control the boiler, not the programmer (Hive or otherwise) The Hive will control the motorised valves. Also, if one boiler has 'voltage free' control, the other has 230V control. Have you determined how are you going to achieve that from the same motorised valves?

    And I'll mention it again, if (which you haven't confirmed or denied) your oil boiler is presently controlling the pump. How do you propose to get it to operate when the electric boiler is running?
     
  10. oilhead

    oilhead

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    Drayton used to make an item, RB2 relay which was used to prevent backfeeding boilers or pumps. Essentially, this was 2 double pole relays. A similar unit could be utilised to feed either/or heat source actuated by the throw of your changeover switch. To a competent 'spark', I'm sure it would be a straightforward job.
     
  11. Maciek

    Maciek

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    Can't answer those questions as have no idea. Was hoping it will be much easier.

    If i can't figure it out, will just re pipe the outlet of the boiler after the existing circulation pump and add another one for electric boiler.

    Will use electric boiler for heating radiators only and oil for heating a water or both when we start running out of electricity.

    Will use separate thermostat just for electric boiler.
     
  12. Maciek

    Maciek

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    Thanks. Will have a look into that.
     
  13. stem

    stem

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    If you were to wire a separate thermostat just for the electric boiler, that would start the boiler OK, [your proposed second pump would also have to be connected to it somehow] But the water wouldn't flow to the radiators because the heating motorised valve would remain closed.

    With an S-Plan the fundamental design is that:

    1) The heating programmer/thermostat will operate the motorised valve.
    2) The heating motorised valve when open, will then operate the boiler.

    You could use isolating relays [as per @oilhead refers to]. The Hive would operate the heating and hot water motorised valves as it should. [the hot water valve via the cylinder thermostat] Then the switches inside the motorised valves [ie those that are there specifically to control the boiler] could operate relays via a boiler selector switch to provide a 'voltage free' contact for the electric boiler, and '230V' for the oil boiler. If the electric boiler relay were to have a second contact, that could be used to control the pump. Like I said before. It's....

     
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  14. Maciek

    Maciek

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    Water will flow if piped in after motorized valve
     
  15. Maciek

    Maciek

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    Yes. Thank you. on that principle I have solved the puzzle.

    All is wired up and working fine.

    Before I will tell you how I let you try to figure it out. it is very easy if you think outside of the box.

    the only added parts I'm using are 2 way light switch to switch between boilers and second thermostat connected to electric boiler. It should give you enough clues to sort it out,
     
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