Installing a Nest Thermostat

[Steve Wegerle]

Hi all,

I want to have a go at replacing my current combi boiler thermostat with a Nest. I currently have a Potterton boiler installed with a timer and thermostat. I believe the Nest E can replace the thermostat component but I am not sure on the correct wiring. Appreciate if anyone can provide some guidance?

Thanks,

Steve

 

[RandomGrinch]

I believe the Nest E can replace the thermostat component but I am not sure on the correct wiring.

Any Nest can replace your existing thermostat, as there is a Neutral and Live wire available to power it.
The Nest E heatlink is battery powered and wouldn't require the Neutral wire.

What you do will depend on how much repair work to the wall, you can put up with!
Rather than replacing the thermostat, you could put the Heatlink in place of the timer - the thermostat could then be linked out and removed, but that would leave a hole in the wall to repair.

If you don't want to repair a hole, and are happy with retaining the timer in place (set it to permanently on); replacing the thermostat with the Nest thermostat E Heatlink would require these connections:

The brown wire in Com, would go to Heatlink C.
The black (oversleeved brown) wire in H, would go to Heatlink NO.
The grey (oversleeved blue) wire in N, would need to be safely isolated in a separate terminal block.

 

[ericmark]

@RandomGrinch has answered your question, however I have found Nest Gen 3 thermostat rather useless, as it does not do what it says it can do, which is connect to the Energenie MiHome TRV heads:-
1) It can be controlled by the MiHome app, but the wall thermostat and the TRV will not follow each other in any meaning full way.
2) The geofencing allows you to set Eco and Comfort temperatures, but not the distance from home when it swaps between the two setting.

So I now have a Wiser thermostat set in parallel with the Nest, so that TRV heads can activate the boiler. My Nest now only does DHW, clearly Nest e does not do hot water anyway.

Yes Nest has allowed me to see the temperature to gradually raise through the day 0.5ºC at a time, with 2 hours between each rise, but had it worked with the TRV heads, I would not have needed to do that anyway. It sends me a history but since that is only how long calling for heat, not how long the boiler ran for, rather useless.

Nearly every feature of the Nest Thermostat I have found I needed to turn off. The Wiser thermostat app at least does give some useful info, as does the Kasa TRV head they do help work out what if anything is wrong, but only good point for Nest is it can be controlled from PC without a emulator.

 

[Steve Wegerle]

Thank you both; I'll have a go and report back on how it works out

 

[ericmark]

I am watching, as interested to see how it works for you.

 

[ChrisJP]

Maybe I'm too "old school", but I'm puzzled by the enthusiasm for Nest thermostats and their like, given their complexity and, as noted here, sometimes failure to do what they claim.
I have a timer with the CH switched permanently to ON (I use the timer to switch HW on and off at set times). The boiler is then controlled by a programmable thermostat which I've set to 16C during the day and uring nightimes, rising to 20C half and hour before I normally get home and for the evening and again an hour before I normally get up for the period before I normally leave home.
The thermostat is a 7 day one, so I can vary these times for weekends. I can of course easily increase the temp on this thermostat any time I want a bit of extra heat, and it will return to its settings when it gets to the next programmed change in temp.
My radiator TRVs are not of course controlled by anything other than their attached adjusters, but I've set them up and don't feel any need to constantly change these settings.
Sure I can't control all this over the internet using my cellphone, but I've never found I wanted to do this, and I can't think of any reasons why I'd want to mess with the settings when I'm outside the house.
Sometimes I suspect these internet based controllers are solutions looking for problems!

 

[RandomGrinch]

It's a complicated subject.
Eric is well known for his anti-Nest views
I have a 2nd gen Nest and really like it -
It suits our family and our house - I can see Eric's argument for why it doesn't suit him, but that doesn't mean it won't be right for others.
It's a nice intuitive thing to use and looks good.
I use the app occasionally - i.e. if I'm in bed and feeling a little cold and a little lazy, I can bump the heating on for a bit, without moving.
Or, from experience, in mid-winter with a newborn, when you've unexpectedly stayed in hospital for 5 days; coming home to a warm house is extremely welcome!

What is also forgotten with smart stats, is that they can also save energy. Even without a modulating boiler or controls, a smart thermostat can perform "on/off load compensation", i.e. it's smart algorithms know how long it will take to warm your house, given the external temperature (that it knows from internet forecasting and other local users in the network). This allows for more precise control of on/off times, leading to a better steady state temperature and efficient use of gas.
In some recent research, it was found modulating controls could gain 12% efficiency, whilst smart stats without modulation, could still save a credible 10% through load compensation, over an ordinary 'dumb' stat.
And I think this is what I appreciate best - it is very good at keeping my house at a steady state temperature.
Apart from that, it's horses for courses!

 

[ericmark]

I have programmable TRV heads in mother's house, and will admit it took some time to set the lock shield and TRV's, but once set it worked A1.

To save energy, we want to heat just enough, and no more. But also allow the minium of heat to leave the flue. For the latter, we want to run the boiler as cool as we can, the more water which has released its latent heat the better, so cooler the flue gases the more latent heat gained.

So the boiler needs to be allowed to modulate, (turn down) to gain this latent heat, and every time we turn off the boiler with an on/off control, the boiler has to start again setting how much it can modulate by, so we only want to turn the boiler off after it has fully modulated.

So if the boiler can use OpenTherm, then thermostats like Nest and Wiser are far better as they turn boiler up/down not on/off. But since I use oil, and it does not modulate, this feature is wasted for me.

The idea of the Nest Gen 3 is it will learn what you want. But to do that, the home needs to behave the same all the time. Leave a door closed one day, and open the next, and it does not know what to do, in my old open-plan house it would have worked well, but this house has doors to every room.

 

[Steve Wegerle]

Just following up on my original post, I've followed the instructions as per RandomGrinch and it's worked perfectly, all now set up and installed in under 30 mins. Very easy job, thanks again for the help!