Discuss How do I fit a digital thermostat? in the Central Heating Systems area at ElectriciansForums.net


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Hi everyone
I am hoping someone can offer me some advice.
I would like to get a digital thermostat (something like a Nest, but I am open to suggestions on this). However, I am a little unsure on how I would fit it.

Does it go in place of the digital thermostat (Drayton, in picture 1) or the thermostat dial (British Gas, in picture 2). I am not entirely sure that the dial still works as it never lights up. I took the cover off today and it's warranty ran out in 2004 (we moved in to the property in March).

Any advice would be gratefully received.

Kind Regards



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Basically, a Nest or a Hive type system replaces both of the items that you show in your pictures.
How easy to fit depends on the type of central heating system you have.
I.E Type of boiler, do you have a hot water cylinder or is it a combi? If you have a cylinder is it pumped or gravity, etc.
It is not usually that difficult to do, but you do need to understand what you are doing


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The Drayton device is a 7 day programmer, not a thermostat and is often positioned close to the boiler or airing cupboard, not in an ideal place to control room temperature.
Your room temperature is probably controlled by the BG dial thermostat irrespective of it illuminating or not. Furthermore individual rooms may be controlled by TRV's (Thermostatic Radiator Valves) on the actual radiators leaving the BG thermostat virtually redundant but would still have overall system control!
The replacement device if programmable thermostat needs to be positioned in such a place to best monitor room temperature but again if TRV's fitted will only provide general overall control.
Positioning may depend upon what wiring you already have or what wireless controls you purchase.


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Thanks Andy-1960 and DefyG.
The boiler is a combi. So could I potentially just using the wiring for the BG dial to wire the nest? It is central in the hallway whereas the 7 day programmer is by the back door.
The Nest installation video makes it look too easy to fit so there must be a catch surely.
Thanks again
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Are you certain it’s a combi? You have a dual channel programmer (Drayton LP722). No you can’t use the wiring alone as Nest needs a permanent live and permanent neutral. If indeed it is a combi, then you can use the wiring at the Drayton programmer for the Nest heatlink, and use the wiring at the BG (Drayton ) room thermostat for the Nest thermostat.
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OK digital is old method i.e. on/off, analogue new method turns boiler output up down, the modern boiler can adjust output up/down and two main methods, one connects to boiler ebus, the other controls return water temperature.

The latter method has a problem, unless pump and boiler is running, it can't work, so it needs another method to turn boiler off in warm weather, so a simple on/off thermostat is used, it should be placed in a room on ground floor, normally kept cool, with no outside door, or alternative heating.

Often there is no such room, so some compromise is required.

However the point is, often to swap, means located in different room, and connected to different place in the boiler, so the first question is what boiler? Worcester Bosch for example is very limited as to what it will work with, it does not have OpenTherm.

And controlling the home with TRV heads can work out better than using a single wall thermostat, so what are you trying to do?


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Thanks for your advice Boiler Repairs and Eric Mark.
I had a go at it yesterday. The heat link has been installed in place of the thermostat and the original programmer is set to always on. All seems to be working as it shoud at the moment. I will probably look at a way to bypass the programmer completely in the summer but I don't want to risk losing the heating mid winter. The instructions on the nest app were extremely in depth.
Thanks again.

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