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Do I need two mains supplies for boiler and wiring centre?

Former Community Member
Former Community Member

Good evening, Just like to say hello and that I am not a gas engineer or an electrician, but I would just like to understand what I need to ask for. I have a question about an old y-plan central heating installation dating back to 2000. I have an old Gloworm micron 50ff boiler situated in the consumer unit cupboard. However, it is connected to the wiring centre situated in the hot water cupboard 6 meters away via 3 wires, switched live, neutral and earth. I also have an old Grundfoss pump connected into the wiring centre that has only 4 wires, Blue, orange, brown-white, and grey, (I notice new pumps have 5 wires). The pump also has 3 settings using 40,65 & 95 watts. I also have 3 port mid-position valve, room stat, hot water stat and 2 channel programmer, (all from Danfoss heatshare pack).



 



Due to limited access in consumer unit cupboard I am limited to fitting either a Worcester greenstar ri series boiler or a Baxi ecoblue advance. Looking at the wiring diagrams, with my limited understanding, does fitting the Bosch require separate mains supplies in each cupboard, one for the boiler and one for the wiring centre and will the pump kill the boiler using an extra 5 watts as the worcester boiler is rated at 90 watts, and could I still use it with only 4 wires or would I need a new 5 wire pump too.



 



Or would it be better to go for what seems to be the simpler option of the Baxi as it requires no pump overrun or permanent live and looks as though it is fed with just live, neutral and earth from the wiring centre as I have now.



 



Sorry about the long question, and many thanks in advance. Simon.


  • Hi Simon you really need to let a professional heating engineer sort this for you  it's a bit of a minefeild trying to sort all this out  and unless you are quilified to do it it can quickly get very complicated. If you have any choice in the matter go for the Worcester boiler they are generally very reliable  the one here at Kelly towers runs very well even after 5 years hope this helps a bit
  • No, you dont put two supplies in, for boiler and wiring centre. One supply feeds it all.

    And most importantly, one switch turns it off and can isolate it all.

    I dont know why you think new pumps have 5 wires, all the ones I've fitted have 3, LNE.

    Pump overrun is done at the wiring centre, with an extra wire from the boiler.

    Don't choose  a boiler by how many wires it has going to it (most have - permanent LNE, Switched live, and pump overrun).

  • alanblaby:

    No, you dont put two supplies in, for boiler and wiring centre. One supply feeds it all.

    And most importantly, one switch turns it off and can isolate it all.

    I dont know why you think new pumps have 5 wires, all the ones I've fitted have 3, LNE.

    Pump overrun is done at the wiring centre, with an extra wire from the boiler.

    Don't choose  a boiler by how many wires it has going to it (most have - permanent LNE, Switched live, and pump overrun).




    Not quite Alan, I would agree that is the most common way, but have a Worcester Bosch Greenstar and the pump overrun is at the pump itself.


    Regards.

  • Former Community Member
    0 Former Community Member
    Good Afternoon, Thank you for your replies to my completely messed up question, much appreciated. I feel like a right dummy!  What I meant to say was that my old Danfoss 3 port mid-position valve has only 4 wires coming out of it, and would I still be able to use it with a new boiler?  Everyone is right, my pump only has 3 wires. I must admit I'm inclined towards Worcester as they seem to have good reliability scores, It was the potential problems, as I saw them, with installation that worried me.


    Kind regards, Simon
  • If the valve switches from hot water to rads properly, then you can re-use it - the boiler does not care, so long as it has power and a line that goes live to say 'light the fire now'.

    The valve and various thermostats are interlinked to provide that signal, so if the water is cold, and the valve is in that position, then fire, or if the room stat is cold and the valve is in the other position then fire...


    One or other of your thermostats will need a back contact, so that it can report 'demand for heat' and also 'no demand for heat = satisfied' to force the changeover.

    This is normally best explained in the instructions for the combined heat and water timers.


    It is just mains level logic, but it can be quite confusing, as there as the equivalent of a not and = or not.

    As a personal opinion, I'd go with the Bosch if you can afford it, I've had one for ~ 15yrs now and it has just had its first fault.



  • mapj1:

    As a personal opinion, I'd go with the Bosch if you can afford it, I've had one for ~ 15yrs now and it has just had its first fault.




    All that shows (he says mischievously) is that Bosch we're good 15 years ago. ?


    Some maintenance has been required, and I don't want to tempt fate, but our Ideal boiler (which doesn't actually boil anything) has been going for 37 years. Floor-standing cast iron and none of that condensing nonsense! ?


  • burn:




    alanblaby:

    No, you dont put two supplies in, for boiler and wiring centre. One supply feeds it all.

    And most importantly, one switch turns it off and can isolate it all.

    I dont know why you think new pumps have 5 wires, all the ones I've fitted have 3, LNE.

    Pump overrun is done at the wiring centre, with an extra wire from the boiler.

    Don't choose  a boiler by how many wires it has going to it (most have - permanent LNE, Switched live, and pump overrun).




    Not quite Alan, I would agree that is the most common way, but have a Worcester Bosch Greenstar and the pump overrun is at the pump itself.


    Regards.


     




    burn how would the pump know when to overrun or not, all the ri's that i have wired require a connection from the boiler for the pump thus a 5 core between the boiler and the wiring centre.

    Back to the op question, is it hard to get a new wire from the wiring centre to the boiler? if so then go with the Baxi, if not go with the Worcester.

  • Worcester Bosch specifically tell you to take the mains supply into the boiler then take the supply to the wiring centre from the boiler,  so that when you turn the boiler off if disconnects the whole of the control wiring. 


    Safe and simple wiring.


    Andy Betteridge

  • Sparkingchip:

    Worcester Bosch specifically tell you to take the mains supply into the boiler then take the supply to the wiring centre from the boiler,  so that when you turn the boiler off if disconnects the whole of the control wiring. 


    Safe and simple wiring.


    Andy Betteridge 




    New one on me Andy I have never seen that in the installation manual, all it says is

    The mains supply to the appliance and system wiring centre must be

    common, and through either a fused double pole isolator or a fused

    three pin plug and unswitched socket.

    The isolator/socket, where practicable, should be situated next to the

    appliance.

  • That came from conversations with their technical helpline and service engineers.


    On the board within the boiler there are a permanent live, neutral and earth connections to supply an external programmer and for an external circulation pump, if required because a prewired internal circulator has not been installed within the boiler.


    The off switch built into the boiler should disconnect the power supply to the boiler along with the external controls and any circulation pump.


    Andy Betteridge