2 x central heating boilers wiring ??

[Maciek]

Hi. Looking for a bit of advice.


Currently running an oil fired central heating boiler and planning to add another central heating boiler which will be electric. Both boilers will be open vented and feed from the tank in the loft, at least for now. The installation might be converted to sealed in the future. Both boilers have options to run either of them.

As for the plumbing don’t really see a massive issue but have no idea how to wire them so it makes some sense, preferably one unit that will allow us switching between oil and electric. Preferably one thermostat as well, currently running hive.

Found something like that https://www.nrgawareness.com/product/nrg-lex-system-control-module/

There will be no zones, just heating provided for a full house switchable between oil and electric. Anyone can help?

 

[flameport]

If you just want to use one boiler or the other, then you just need a switch in the switched line from the controls - a common input from the controls, and 2 outputs, one to each boiler.
Such as any 2 way light switch.

Why would you want a hideously expensive electric boiler when you have oil available?

 

[Maciek]

If you just want to use one boiler or the other, then you just need a switch in the switched line from the controls - a common input from the controls, and 2 outputs, one to each boiler.
Such as any 2 way light switch.

Why would you want a hideously expensive electric boiler when you have oil available?

I was thinking about the switch but thought there might be different options.

Only one boiler will be used at the time.

We do produce hell lot of electricity so we can use it better than now.

 

[Dan Robinson]

Use a timer to act as a changeover switch.

 

[stem]

You may have to think about the pump from a controls point of view. For example, if one of the boilers has an integral pump, or a pump overrun which requires the pump to be connected to the boiler for its control.

 

[Maciek]

That will cause an issue. Is there a solution to overcome that ?

 

[stem]

If there were to be one separate pump that is not an integral part of either of the boilers & neither of the boilers need to control it (ie to provide a pump overrun), and as such it is controlled by external sources, (e.g. a motorised valve) then there is no issue, and a boiler changeover switch as has been proposed will be OK.

On the other hand, if one of the boilers has a pump internally, or needs to have control of the pump, in that the pump is wired to dedicated pump terminals inside the boiler, then when the changeover switch was operated the pump wouldn't work anymore because it is wired to the boiler that is no longer in service.

I don't think it's a deal breaker, you just should bear it in mind. Probably the easiest way to overcome it would be for the second boiler to have its own dedicated pump also.

These are just electrical observations, I'll leave the plumbing experts to comment on any mechanical issues.

 

[Maciek]

Oil boiler that I'm using is Grant vortex eco external system 21-26 so as far as I'm aware there is no internal pump. I have 2 motorized valves changing between CH and HW and circulation pump for CH.

I can buy an electric boiler without pump so that should solve any potential problems if that make more sense.

 

[Maciek]

Finlay managed to plumb both boilers together. Now need to wire them but need to ask someone for help.

I like the idea of a switch between 2 boilers as only one will be used at the time. There is only one circulation pump and current oil boiler is wires to the junction box. Pictures below.

This is an electric boiler inside which has a plug to wire the thermostat. I'm using 2 channel hive for heating and hot water.

Plug after disconnection, has 2 spare terminals

Wire junction box where call and common are bridged together for hive

Very unhelpful manual that came with the boiler

Now for the fun part. How to connect two way switch to be able to switch between 2 boilers and leave hive do the rest ?

 

[AGAS]

Makes me laugh when people attempt wiring when they haven’t a fooking clue just why ???????

 

[Maciek]

Ok. You said what you need to. If not willing to help just stay quiet.

I hope someone will be able to help.

 

[bsr]

It would help if you explain why you want two boilers. Is it because you have solar and want to use it to heat water rather than export it?

If so, look at iBoost or similar devices. They make more sense.

 

[Maciek]

Yep. house is off grid and we do produce way to much that we can use or store so needs to go somewhere. We do not produce enough to have electric heating only so we have oil.

It is all plumbed and connected to electricity. Just need to know how to wire it to current system so I can easily swap between boilers using a switch. If not possible I will just put second thermostat and will turn oil boiler off when using electric.

 

[AGAS]

Ok. You said what you need to. If not willing to help just stay quiet.

I hope someone will be able to help.

Don’t come crying when you’ve shorted something

 

[Maciek]

Don’t come crying when you’ve shorted something

Don't understand whats the point of your childish coments?

If you know how to wire it, you could use same effort and just tell me, unless you just prefer not to