Nest thermostat

[Declanmcmahon18]

hi,

I'm getting a nest thermostat fitted by a local gas engineer but he's telling me that the voltage is too high coming through where the original thermostat was fitted and he wants me to put the nest on a stand?

Does this sound right? He's saying that the nest won't turn on because of the high voltage.....

 

[Dan Robinson]

Get another installer.

 

[Declanmcmahon18]

Really? Is this bullsh*t?

He was ages trying to get it to turn on but gave up for a finish.

 

[Gorners]

The Nest needs 12v, not 230v - there’s a big warning label around it when you take it out the box. If he’s only just realised the voltage is too high then he’s created you a nice paper weight

 

[muggles]

If he's put 230v into your Nest, he's almost certainly fooked it. Time to get a new installer, and probably a new Nest too

 

[ericmark]

Old systems tend to have a junction box, this allows connection between motorised valves, thermostats etc. Also a programmer (time switch) and nest heat link tends to replace the programmer, there are 4 extra connections to the normal programmer. OT1 and OT2 are only used with new boilers, and T1 and T2 is simply a supply for the thermostat, in some cases the cables can be reused and what originally went to thermostat can instead supply the actual thermostat, however where you can't do that, it can be powered from a USB socket.

I will guess the stand supplies the 5 volt required in an easy way to connect, however still need a USB supply. There is it seems a battery-powered model comes with six AA batteries that Nest says will last five years, while the wired version comes with three AA batteries that are meant to serve as a backup if your electricity goes out.

It does seem a common problem being able to get the extra low voltage supply required, however one would hope a professional would know methods of neatly getting this supply.

There are two completely different ways to connect nest, for older boilers it simply switches the boiler off/on, but with more modern boilers it turns the boiler output up/down to suit demand making the control hysteresis free and more economical. If the installer does not know how to power the thermostat, it seems unlikely he will know how to connect to boiler bus to use the opentherm option.

I would be looking for another installer who knows what they are doing.

 

[Declanmcmahon18]

He was saying that it’s getting around 17v which is too high and won’t let it switch on.

As mentioned above, nest only requires 12v. Is there anyway to reduce the voltage down to the 12v required?

I don’t want to have to use a stand. I’d prefer to stick with the old thermostat than get a stand.

 

[stem]

I'm getting a nest thermostat fitted by a local gas engineer but he's telling me that the voltage is too high coming through where the original thermostat was fitted and he wants me to put the nest on a stand

It may be plausible, but he has probably been a bit simplistic in his explanation, so I'll try to expand.

The original room thermostat most likely will be connected to 230V, but instead of decommissioning it properly when installing Nest, some installers leave it, and its wiring in place and just bridge the wires to prevent it interfering with the operation of the new Nest. Why? Because it's easier to do, and saves them work. So, if this is your installers modus operandi, then they are correct; there will be 230V on the old thermostat wiring, and as has been pointed out, the Nest thermostat needs 12v to operate.

The 12v supply for the Nest thermostat can come either from wiring it directly to the Heat Link which has a built in 12v power supply, or from a separate plug in power supply as has been suggested by your installer.

However, if the old thermostat is decommissioned properly, then the existing thermostat wires will no longer be connected to 230V and can then be used to connect the 12v from the Heat Link to the Nest thermostat. But that is not always as easy as it sounds. Depending upon how the original thermostat wiring is connected it may not run to the same location as the new Heat Link and so may need rerouting / extending anyway.

EDIT:
Sorry, your last post came in whilst I was typing so didn't see it until I had posted the above. So based on that, then I refer you back to Dan's original post.

Get another installer.

 

[Gorners]

So where are the wires connected at the other end? As in, the ones carrying 17v, where is that coming from - the boiler? I’m assuming it’s not connected to the heat link, if it is then it’s probably faulty.

 

[ericmark]

If you want to DIY then give some information as to what you have, there are many systems, many have a type letter, C, S, W, or Y but we don't know if your system has motorised valves, if it heats domestic water direct or with a cylinder, "stem" is really good, but he does not have a crystal ball, you have to give some description of what you have.

 

[Declanmcmahon18]

Don’t want to DIY at all Ericmark.

Simply questioning what a professional has told me as it sounded bizzare.

Gorners - the wire is currently coming from the water cylinder which is upstairs. When the nest wouldn’t turn on, he connected it to the heat link for now so that I can use it.

So in summary, regardless if he is getting 17v from the original wires, he should be able to work around it to reduce the voltage and put the nest thermostat where my original thermostat was on the wall and there is no need for a stand! Is the what I’m feeding back to him?

 

[Dan Robinson]

Sadly not all professionals have a scooby doo when it comes to system electrics.


When Nest first came out and every bloke with a spare £150 wanted to have the next best thing, installers like me did a very good turn out of going around mopping u the pieces left by muppets like your guy.

Remember one firm running around not knowing the difference between mains switching and volt free switching. 230v down the wrong side of a boiler PCB can end up with lots of fizzing and popping Cost one customer (who claimed back from Nest I suppose) nearly £600 in additional work and repairs as they had blown the board on a boiler when all they needed to do was reposition one wire in the wiring centre and then reuse the existing two thermostat wires. Would have taken 10 minutes to have done it correctly the first time. Ended up taking two hours total. Plus the original 10 minutes

 

[stem]

regardless if he is getting 17v from the original wires, he should be able to work around it to reduce the voltage and put the nest thermostat where my original thermostat was on the wall and there is no need for a stand! Is the what I’m feeding back to him?

Sorry, but that makes no sense to me whatsoever. An installer cannot 'change' any voltages, the voltages are what they are. You have to work with what is there.

1) The Nest Heat Link requires 230V mains to provide it with the power to operate.

2) The Nest Thermostat requires 12v to operate. This can come from the Heat Link terminals (T1 & T2) because the Heat Link has a built in 12v power supply, or the 12v can come from a separate plug in power supply.

3) The Heat Link has voltage free contacts (ie a switch) to control the heating (and hot water if you have a hot water cylinder) so can switch any sensible voltage you connect to them. eg. 230V, 12v, 24v, 17v??

Where's this 17v coming from?

 

[Gorners]

When the nest wouldn’t turn on, he connected it to the heat link for now so that I can use it.

Are you sure you mean the heat link? Or the USB plug? The USB plug isn’t the heat link - that’s the square thing which should be right next to your boiler wired into it. It’s from there where the 12v supply can be taken to the thermostat. If that’s indeed what he’s done, as you say, then what’s wrong with this set-up?

 

[Declanmcmahon18]

Gorners - He connected it to the heat link which sits under my boiler in the utility room. It’s just a temporary measure so that it’s useable.

I don’t want my nest thermostat to remain there. I want it in my hallway on the wall where the original one was.


Stem - the 17v is a reading he was getting from where the original thermostat was placed in the hallway. It’s a cable that comes from where the water cylinder is housed upstairs.