Fitting Nest Direct Power

[ChrisPembs]

Hello, in need of some help please, bought a Nest 3rd Gen Learning Thermostat Kit, currently have an oil fired external combi boiler with a Honeywell Home Programmer and wired thermostat, the thermostat will become redundant and I need to replace the programmer with the new Nest heatlink, all good so far, wiring seems straight forward just a basic install for me.

Now, from the videos I have seen the feed wires for the heatlink comes from the boiler in most cases including the power, so usually boiler power to a switch, from switch tot he boiler, then from boiler tot he programmer, in my case the switch power comes into the programmer then there is a wire that goes from the programmer to the boiler outside.

Have attached a photo below, I am assuming I just need to do the exact same thing in the heatlink? So the grey mains wire goes to the old room thermostat so that will be scrapped but the wire from the switch live neutral and the wire live neutral going to the boiler both together in the same normal live an neutral terminals on the heatlink?

Thanks in advance, think I am way over thinking this but wanted to make sure before blowing the boiler up

 

[RandomGrinch]

currently have an oil fired external combi boiler with a Honeywell Home Programmer and wired thermostat,

What model is the Honeywell Home programmer?
I may be wrong, but it looks like the connections are for a hot water and heating programmer.

 

[ChrisPembs]

Hi and thanks for the reply, it is a Honeywell ST9400C 1000, the programmer can control water as well I believe but with us having a combi boiler it made no difference what the water was set to the boiler did its thing and provided it, when we moved in the previous owners told us that the installer had explained to them that the hot water side was not needed?

We seem to have the correct amount of wires for a basic combi install once the wired thermostat is out of the way and also the power in the wires going to the boiler are the usual L N E and the black and grey signal wires, the complication for me is the power being fed to the programmer and not directly to the boiler, as said I am assuming I just need to do the same as it is with the honeywell so the 2 lives and neutral together in the one terminal but just wanted to try and confirm that.

Thanks again.

 

[RandomGrinch]

Honeywell ST9400C 1000, the programmer can control water as well I believe but with us having a combi boiler it made no difference what the water was set to the boiler did its thing and provided it, when we moved in the previous owners told us that the installer had explained to them that the hot water side was not needed?

Ok, that sort of explains it!
The programmer is a two channel programmer, and the black wire going into ST9400C terminal 3, is the Hot Water On connection.

Sometimes a combi may have a small thermal store, or it's possible this wire was a remnant from a previous installation?

Anyway, if you have a combi, never touch the hot water programmer, and haven't noticed a problem, I think we can safely ignore it!

So after removing the grey thermostat cable...

Connect the 2 Blue wires in N on the ST9400C, to N on the Heatlink.
The 2 Green/Yellow earth wires in the earth terminal to the Heatlink earth terminal.
The grey wire currently in the separate terminal block, would connect to Heatlink
terminal 3.
The terminals are a little tight to fit multiple wires on the Heatlink, so you can put one brown wire from the L on the ST9400C into terminal L on the Heatlink.
Put the other brown wire into terminal 2, and then use a short link wire to connect L and terminal 2 on the Heatlink.

For the sake of completeness, the black 'Hot water on' wire in terminal 3 of the ST9400C can be placed into terminal 6 of the Heatlink.

If you intend to power the Nest thermostat from the Heatlink, the 12V power cable would connect into terminals T1 and T2.

I hope that makes sense.

 

[ChrisPembs]

That makes perfect sense, thanks, appreciate it

 

[ChrisPembs]

Ok, that sort of explains it!
The programmer is a two channel programmer, and the black wire going into ST9400C terminal 3, is the Hot Water On connection.

Sometimes a combi may have a small thermal store, or it's possible this wire was a remnant from a previous installation?

Anyway, if you have a combi, never touch the hot water programmer, and haven't noticed a problem, I think we can safely ignore it!

So after removing the grey thermostat cable...

Connect the 2 Blue wires in N on the ST9400C, to N on the Heatlink.
The 2 Green/Yellow earth wires in the earth terminal to the Heatlink earth terminal.
The grey wire currently in the separate terminal block, would connect to Heatlink
terminal 3.
The terminals are a little tight to fit multiple wires on the Heatlink, so you can put one brown wire from the L on the ST9400C into terminal L on the Heatlink.
Put the other brown wire into terminal 2, and then use a short link wire to connect L and terminal 2 on the Heatlink.

For the sake of completeness, the black 'Hot water on' wire in terminal 3 of the ST9400C can be placed into terminal 6 of the Heatlink.

If you intend to power the Nest thermostat from the Heatlink, the 12V power cable would connect into terminals T1 and T2.

I hope that makes sense.

Hello, Ok a bit more progress made, the wire coming from the switch and also to the boiler is copper strand, I noticed in the instructions Nest say do not use this and thought I had no chance of getting 2 stranded wires into the Heatlink terminal so found some 1.5mm solid copper core wire and got the Wagos out so now the 2 lives, 2 neutrals and 2 earth go into wagos with 1 solid copper core coming out for each one which I have wired into the heatlink, the heating works fine full control vi the thermostat, the app and also Alexa the problem I am now having is with the hot water, tried the black wire in all 3 hot water terminal and nothing seems to make any difference however, I noticed in your post you mentioned some combis have a small thermal store, this one does so not sure if that makes a difference to the way it needs wiring?

There is some hot water coming through and the hot water pump in the boiler is powering on, the heat of the water is nowhere near what is usually is however and fluctuates quite a bit, this boiler produces roasting hot water really quite well so a bit stumped, I am assuming the boiler is not cycling to keep the thermal store hot as I have noticed when the heating is powered on the boiler comes on immediately, usually it pump around whatever is in the water store first then after a few minutes the boiler fires.

Hope I explained that well lol and thank you again.

Forgot to mention, my boiler is a 230v so did add the link wire from the live to terminal 2 even though I had wago'd the 2 lives already, this made the heating work.

 

[RandomGrinch]

I am now having is with the hot water,

Ok.

Anyway, if you have a combi, never touch the hot water programmer, and haven't noticed a problem, I think we can safely ignore it!

So previously, you probably did touch the programmer to get hot water!

For the sake of completeness, the black 'Hot water on' wire in terminal 3 of the ST9400C can be placed into terminal 6 of the Heatlink.

And also add a link wire between L and terminal 5 of the Heatlink.

the wire coming from the switch and also to the boiler is copper strand, I noticed in the instructions Nest say do not use this and thought I had no chance of getting 2 stranded wires into the Heatlink terminal

There's no real issues using stranded copper in the Nest terminals - a lot of thermostat wiring is done with flex instead of T & E, and it's fine with it.

 

[ChrisPembs]

Hey thanks for the quick reply So a link wire from L to terminal 5 then the grey wire left in terminal 6?

I never remember doing anything with the old programmer at all, when we moved in for completeness I switched both to constant and then if we ever wanted heat we used the mechanical thermostat, in hindsight it looks like the water side actually needed to be set to constant to work and I had never really noticed as never touched it, apologies lol

 

[RandomGrinch]

Hey thanks for the quick reply So a link wire from L to terminal 5 then the grey* wire left in terminal 6?

*Black

in hindsight it looks like the water side actually needed to be set to constant to work and I had never really noticed as never touched it, apologies lol

 

[ChrisPembs]

Ok I think we are winning lol, link wire from L to terminal 5, GREY (lol) wire to terminal 6< still not cycling to heat the store and not hot water, sheer devilment had me move the grey wire from 6 to 4 and boom, working perfectly so far, boiler cycling, heat store hot, when call for heat it is using the heat store first then firing the boiler after around 4 minutes, working completely as before so I think I can call it installed.......

Only thing not working is the green lights on the heatlink so when the thermostat is turned up and call for heat I was expecting the heat light to light green, similarly when you switch the hot tap on I thought the tap light would light green but neither do, if I press the override button they both illuminate but not under normal control, maybe I have misunderstood what those lights do lol

Anyway, thank you so much for your help, I really really appreciate it

 

[RandomGrinch]

Ok I think we are winning lol, link wire from L to terminal 5, GREY (lol) wire to terminal 6< still not cycling to heat the store and not hot water,

Then did you set hot water to on, in the Nest app, or via the stat?

sheer devilment had me move the grey wire from 6 to 4 and boom, working perfectly so far,

Your hot water store will now turn off, when you turn the water on in Nest!

Glad it's working though.

Only thing not working is the green lights on the heatlink so when the thermostat is turned up and call for heat I was expecting the heat light to light green, similarly when you switch the hot tap on I thought the tap light would light green but neither do, if I press the override button they both illuminate but not under normal control, maybe I have misunderstood what those lights do

They only illuminate when called for manually on the 3rd gen Heatlink...

Heat Link lights and what they mean - Google Nest Help

The lights let you know if Heat Link is connected to your Google Nest thermostat. If it’s disconnected and you need to turn on manual heating, the lights will tell you when your system is runnin

support.google.com

 

[ChrisPembs]

Then did you set hot water to on, in the Nest app, or via the stat?

Your hot water store will now turn off, when you turn the water on in Nest!

Glad it's working though.


They only illuminate when called for manually on the 3rd gen Heatlink...

View attachment 357698

Heat Link lights and what they mean - Google Nest Help

The lights let you know if Heat Link is connected to your Google Nest thermostat. If it’s disconnected and you need to turn on manual heating, the lights will tell you when your system is runnin

support.google.com

I set the thermostat up as a combi boiler so there is not hot water control nest side, I did reset the thermostat and set it up as "other" with hot water control but even then there way no way of operating the hot water, it still only gave me heat option which is why I came to the conclusion for the sake of not going mad and pushing your patience ha ha ha shove it in 4 and see what happens, I understood it would basically be powered on all the time but thought the internal boiler control would do its thing as before, so far so good, fingers crossed ha ha ha

The house is an ex local authority and the boiler was fitted by them so there is likely a level of douchebaggery gone on anyway with the install to match all the other dounchebaggery maintenance that I am slowly undoing, anyway, thank you, star man