Upgrade Nest to Nest v3

[terryhawkins]

I've had the Nest thermostat for a couple of years and now looking to upgrade to v3 with hot water control. My biggest problem now is the mess of wiring that is my heating controller.

The heat link is currently in the airing cupboard wired like this:

And this the mess of wiring at my Potterton EP2001 programmer (probably not as bad as it looks):

Ideally I would like to replace the programmer with the heat link as the programmer is ugly, however I don't mind leaving the programmer set to always on and ignoring that it's there if that's the easiest solution.

But does it look like an easy upgrade, I have no idea what the other wires in the airing cupboard connection do.

I do know that the 2nd terminal down on the block is live when the heating comes on and that the 3rd terminal down is live when the hot water comes on.

Any help would be appreciated.

 

[stem]

First of all yours is probably one of the neatest EP2002's I have seen, so no need to apologise.

The easiest way to install the new Nest, would be to remove the existing Heatlink thermostat wires from the wiring centre and then add a link between the 'live from programmer when heating is set to be on' terminal and 'call for heat' terminal together. This will result in the motorised valve white wire being electrically connected to terminal 4 of the EP2002.

Then replace the EP2002 with the new Heatlink. The wires at the EP2002 can be identified from the diagram below.

So,
Red wire in EP2002 Terminal 1 'HW off' = Goes to Nest 'Hot water satisfied' (4)
Yellow wire in EP2002 Terminal 3 'HW on' = Goes to Nest 'Hot water call for heat' (6)
Blue wire in EP2002 Terminal 4 'CH on' = Goes to Nest 'Heating call for heat' (3)

The wire link presently between terminals EP2002 L & 5 can be discarded.

The 230V supply is fairly straight forward.
The wires in the EP2002 N terminal go to the N terminal of the Heatlink (As there are 3 wires you may have to add an additional connector to do this)
The wires in the EP2002 L terminal go to the L terminal of the Heatlink(As there are only 2 wires the Heatlink will accommodate them)
The wires in the EP2002 Earth terminal go to the Earth terminal of the Heatlink (As there are several wires you will have to add an additional connector to do this)

That just leaves the wires in B & C. These terminals are just connectors and have no useful function other than that, so the two wires removed from B will need to be removed from the EP2002 and re-connected together, and the two wires in C will need to be removed from the EP2002 and re-connected together.

EDIT
As per my later post, I forgot to say that new links should be added, connecting the Heatlink 'L' and the two common terminals '2' & '5'

 

[terryhawkins]

Many thanks for the reply, much appreciated, so...

I'm basically linking the two terminals that were once connected to a thermostat (now connected to heat link) at the airing cupboard block, so this is always 'on' as it were and all the rest can be done where the controller sits by swapping cables like for like? Sounds pretty easy.

My next challenge is to get power to my Nest thermostat then, as this is currently powered by the heat link and it's mounted on the wall where my old thermostat was. The cables for this are in the airing cupboard so I can't see a connection route via programmer location.

I could always put a transformer in the airing cupboard for power perhaps? I did struggle to find a permanent live before. Any suggestions?

 

[stem]

I'm basically linking the two terminals that were once connected to a thermostat (now connected to heat link) at the airing cupboard block, so this is always 'on' as it were and all the rest can be done where the controller sits by swapping cables like for like? Sounds pretty easy.

Yes, that's it spot on.

My next challenge is to get power to my Nest thermostat then, as this is currently powered by the heat link and it's mounted on the wall where my old thermostat was. The cables for this are in the airing cupboard so I can't see a connection route via programmer location.

I would avoid buying a non Nest power supply for the 12 supply to the thermostat. It has sensitive electronics and not all power supplies provide a smooth DC supply. Also, Nest don't tell you the polarity of the Heatlink 12v terminals T1 & T2 (ie the + and -) but I guess that you could use a multimeter to find it. If you can get 230V to the thermostat then I would install a 13A socket and plug in the Thermostat power supply provided by Nest.

I forgot to say that the Heatlink L should also be connected to the two common terminals 2 & 5

 

[terryhawkins]

Thanks.

I would rather not have a socket, especially where my thermostat is on the wall and it’s the best place for it so don’t want it on a stand.

If I kept the old heat link just for power would that work? Assuming the new thermostat has the same power requirements.

 

[stem]

Probably, I don't see why not, but unfortunately I can't give you definite confirmation. Only Nest themselves would know the specifications for their power supplies.

 

[terryhawkins]

Just thought I would add some more information as I have just spoken with Nest and it may help out others.

The Nest thermostat can be powered by any 12v power source over the existing thermostat wires, it will need to be at least 0.2A (200mA) as that's what the thermostat draws.

 

[terryhawkins]

Sorry, one more question for you stem.

You said to disregard the link between live and terminal 5. What about the other cable in terminal 5? Link that into the live terminal on the heatlink I assume?

 

[stem]

Ah yes, sorry I missed that, the remaining wire should still be connected to the live, like you said earlier swapping like for like. You could put it in terminal 5 of the heatlink which would be connected to the live terminal via the links.

 

[stem]

Just thought I would add some more information as I have just spoken with Nest and it may help out others.

The Nest thermostat can be powered by any 12v power source over the existing thermostat wires, it will need to be at least 0.2A (200mA) as that's what the thermostat draws.

Thanks, that's helpful, this question has cropped up from time to time.

A bit surprised to hear that though, as there are some rough 12v supplies our there that have plus / minus several volts tolerance. Maybe the thermostat has internal voltage stabilisation.

Also, by any 12v power source I guess that they mean a DC power source and not AC. [The heatlink terminals are marked DC]

Did they advise regarding the polarity. ie is T1 + or -

 

[terryhawkins]

Thanks, that's helpful, this question has cropped up from time to time.

A bit surprised to hear that though, as there are some rough 12v supplies our there that have plus / minus several volts tolerance. Maybe the thermostat has internal voltage stabilisation.

Also, by any 12v power source I guess that they mean a DC power source and not AC. [The heatlink terminals are marked DC]

Did they advise regarding the polarity. ie is T1 + or -

To be honest I didn't ask about DC or polarity as in the Nest manual it says that it doesn't matter which way round T1 and T2 are connected to the thermostat and as you said it's marked DC. Might be worth me double checking.

This is what they actually said when I asked the question and explained what I was trying to do:

Oh, I see. That should be fine as well, you can power it with low-voltage wires from any other source, as long as you really make sure that they are 12v.

I asked about current rating and he went to check, came back with this:

Thank you for waiting, I just checked and it's 0.2A or 200mA.

 

[terryhawkins]

Job done and all working, many thanks Stem for your help.

I added a new fused spur from my immersion tank circuit (it never gets used) which is feeding a 12v LED driver to power the Nest thermostat. The thermostat reports power as 10v but it all works fine.

Heatlink has replaced my EP2001 Potterton controller and I've added a backplate to cover the hole left in the tiles.

 

[stem]

Great job, looks fantastic.

 

[Echo the husky]

Nice, where did you get that backplate? Looks useful.

 

[terryhawkins]

Nice, where did you get that backplate? Looks useful.

It's actually a light switch finger plate from ebay (just flat perspex), I managed to find one with just the right dimensions.

Drilled 4 holes (2 for the heatlink and 2 to fix to back box) then attached the heatlink to it, passed the cables through the back and screwed to the wall.