Nest 3rd Gen Thermostat Wiring to a Fire bird Silver Boiler house.(4 Wires)

Discussion in 'Electricians' Talk' started by NPB1990, Apr 15, 2019.

  1. NPB1990

    NPB1990 New Member

    As per title I currently have a Firebird Silver BoilerHouse C26kW. I recently bought the 3rd Gen Nest thermostat and was hoping to install myself. I'm not an electrician but I do know some basics and was hoping to save a few pennies by doing it myself.

    My boiler is situated outside my house in a hut, and a cable runs to the dining room into a switch and a old APT timer(shown in the images on google drive (cant link images properly)). My issues is that i'm not 100% sure how I should wire the nest heat link up.

    One of the images shows the current wiring in the back of the switch, which has a cable coming from outside with 4 wires in it. Black Brown Earth and Grey, The black and brown go to neutral IN and Live IN and the earth wire goes to the earth. The grey however goes to the timer, and two cables go from neutral OUT and Live OUT to the timer also.

    Where do i put the grey cable on the nest? The live an neutral are simple im just unsure of the Grey cable.

    There is no hot water control in the house, the radiators heat the water and also an immersion heating if needed( I know this can not be wired to nest). The system is a gravity fed system with a hot water tank in the bathroom.

    Sorry for the hassle, but any help would be greatly appreciated.

    P.S I know I should probably get an electrician but moneys tight and trying to save a little.

  2. Risteard

    Risteard Well-Known Member

    Get an Electrician. Nest Pro installers are listed on the Nest site.
  3. spirits are real 2016

    spirits are real 2016 Active Member

    where does the grey cable go to on the timer all you've got at the switch is power in and power to timer you will find the grey wire is probably live to boiler but don't quote me on that all i know about nests is they are for birds.
  4. JC2779

    JC2779 Member

    The grey cable is most likely the switch wire from the timer to the boiler, you can check that by measuring the voltage on the grey cable on that connector block as you turn the timer on and off, or look inside the timer and see which terminal it is connect to. If you have a 3rd Gen Nest the you need to connect L and N out from the switch to L + N on the Nest. Then make a small link and link from L to 2 on ( the terminals are small so it may be easier to take another cable from the switch L out to terminal 2 then connect the grey to terminal 3.
  5. NPB1990

    NPB1990 New Member

    @JC2779 Thank you for the reply, I will try this tomorrow and let you know. Help is much appreciated!
  6. MGW

    MGW Well-Known Member

    Gravity hot water sound like C plan, however over the years the C plan has changed, the original had a 10 program programmer, often a physical as well as electric switch stopped you getting the full 16 programs as you can't turn the domestic hot water off. Neither could you control the temperature of the domestic hot water to anything less than the temperature of central heating water, however it was rather simple, no motorised valves or by-pass valves required.

    As the years went on many added a motorised valve, this allowed one to limit the temperature of domestic hot water, and have central heating without domestic hot water, plus main thing it stopped the boiler cycling, before the addition of motorised valve only way to stop boiler cycling was to only heat domestic hot water twice a day for limited time.

    The other problem with C plan is it relied on switching off pump to stop central heating running, and often the upstairs radiators would thermal syphon and still get hot.

    So today it is hard to find a programmer that has the option of working with old C plan. So likely it would need converting to one of the other plans, we have three options, the Y plan uses a single motorised valve with three ports and gives all options, central heating, hot water or both, the W plan very like the Y plan but either hot water or central heating not both. And the S plan has a motorised valve for every function, however all other plans have pumped domestic hot water heating water, and many require a bypass valve.

    I have not seen a C plan for Nest, as to if with a motorised valve it could be done, I am sure it's possible.
  7. JC2779

    JC2779 Member

    It doesn't really matter what type of system it is the Nest is just replacing the existing time clock / controls to turn the boiler on and off, you may not get the full functionality out of the nest unit as you cant control heating and hot water independently with some systems. But you can still set a schedule to fire the boiler on an off.
  8. NPB1990

    NPB1990 New Member

    I got it wired the way @JC2779 had suggested. It seems to be working, I traced the Grey cable the whole way back to the boiler and I do believe it was the live to the boiler it ended up as a brown wire into the boiler.

    Its not ideal that we cant control the water but may look in the future at changing the plumbing of the system to allow this. We have an immersion heating which we may use in the summer for heating water if costs are not extortionate. Unfortunately the nest has no option for controlling this, but there has been people who have used a WiFi switch or plug to run the immersion via it.

    Ill do a bit more research on it and possibly tackle it later.

    Thanks for all the help and advice, couldn't of done it with out your help!
  9. MGW

    MGW Well-Known Member

    I know Nest works with Energenie MiHome TRV's and they also do relays so it may well be possible to use IFTTT to trigger a relay or 13A socket, however not sure, I thought I could switch the Smart Plug + (MIHO005) with the remote controls used for the light switches and sockets but found no, it will only work with hub. However the MiHome range seems to grow every time I look and also the IFTTT apps to work with it, so hard to keep up.
  10. Cyberman55

    Cyberman55 New Member

    Hi @NPB1990, good to hear you got this working. Would you be willing to share your cable order for the nest. I too have a firebird boiler but i'm having problems getting it turn on. Nest Link and Thermostat are set up but when you turn the heating on, nothing happens. I have attached a couple of images of the cables in the TOWERCHRON QM2 which i am replacing.

    I figured i needed to cable it like follows

    towerchron - nest

    n - n
    l - l
    3 (hw on) - 6 (nest)
    4 (ch on) - 3 (nest)


    Attached Files:

  11. ajohn

    ajohn Active Member

    We will be having a new boiler at some point and i have wondered about this aspect. Answer here is to stick with a radio controlled one so no wires other than local to the boiler. We have been using one for a couple of years now without any problems. Salus. All sorts of prices according to what they offer. Some go for control via a mobile but OTT in my view.

    It's so convenient it's actually saved us money. Retired so have a basic program and just control manually if needed due to weather changes.


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