Upgrade Nest to Nest 3rd gen with HW control. Easy?!

[Robin Engelbertink]

Hi,
I would love to get advice on upgrading my Nest thermostat to the Nest version 3 that controls your HW apart from heating. I have the Nest that just controls your heating.

My condensing boiler is the Glow-Worm Ultracom 38hxi and the Nest Heat link is connected to the boiler and within 1m.
My Honeywell ST9100A programmer is also within 1m of the boiler and Nest Heat Link, is connected to the boiler and controls the HW via a set schedule.

All is working as it should be and I wonder, in case I buy the Nest that can control HW as well, if I can SIMPLY disconnect the Honeywell programmer and connect that same wire coming from the boiler to the new Nest Heat Link?

Let me know if you need more info to make suggestions. I'm happy to help and sure I can complete this DIY project.

Many thanks,
Robin

 

[stem]

Yes, this is possible.



Terminal 1 in the ST9100A diagram above has the same function as terminal (5) 'Hot Water Common' at the Heatlink
Terminal 4 in the ST9100A diagram above has the same function as terminal (6) 'Hot Water Call for heat' at the Heatlink

So, it will just be a matter of swapping them over like for like. You won't need to move the L & N to the Heatlink as it will have its own mains supply there already.

If the wire in presently in terminal 1 at the Honeywell ST9100A is linked to the L terminal then, replicate that at the Nest by linking the Heatlink (L) terminal to the (5) 'Hot Water Common' terminal. Ignore this if there isn't an existing link at the ST9100A.

 

[Robin Engelbertink]

Hi STEM,
Thanks for your quick reply! I'm a newby here and I'm impressed.

I have attached a picture of:
1. My NEST Heat link without the HW control (N used, L used, 1 empty, 2 linked to L, 3 used)
2. My HONEYWELL that just controls my HW: 2 water tanks in the loft, 2 hot water cylinders with immersion heaters 1st floor (Earth, N used, L used, 1 linked to L, 2 empty, 3 empty, 4 used)

So I simply?

• buy the new Nest 3rd gen
• remove the CH wiring from my old Nest and connect in the same way to the new Nest N, L, 2 to L and 3
• remove the Honeywell and connect: earth -> Heatlink earth, N to Heatlink N, L to Heatlink L, linking Heatlink L to 5 (as it's present), both wires in 4 go to Heatlink 6

I hope I'm clear! polease tell me if you have any doubts!

Many thanks

 

[stem]

My HONEYWELL that just controls my HW: 2 water tanks in the loft, 2 hot water cylinders with immersion heaters

Er... a bit worried by this. The Honeywell isn't controlling the immersion heaters is it? You can't connect immersion heaters to a Heatlink.

So, I'm assuming that the Honeywell is wired to your boiler to provide hot water from that and is part of the same 3A fused supply for the boiler and central heating Heatlink. Don't proceed otherwise.

I have attached a picture of:

Sorry I can't see any pictures.

So I simply?
buy the new Nest 3rd gen
remove the CH wiring from my old Nest and connect in the same way to the new Nest N, L, 2 to L and 3

Yes.

remove the Honeywell and connect: earth -> Heatlink earth, N to Heatlink N, L to Heatlink L, linking Heatlink L to 5 (as it's present), both wires in 4 go to Heatlink 6

Sort of, but there's no need to move the L N & E from the Honeywell to the Heatlink, there will already be L N & E connected to it. Just disconnect and remove the wires providing the 230V supply to the Honeywell. [An exception to this is if the Heatlink receives it's 230V supply from the Honeywell in which case you will need to move it.] The end result is that you need only one L N & E to the Heatlink.

You then only need to move the wire from.

Terminal 4 in the ST9100A to terminal (6) 'Hot Water Call for heat' at the Heatlink

Insert the link between Heatlink 'L' and terminal (5) 'Hot Water Common' [You can use terminal (2) instead of (L) if it's easier. The end result will have Heatlink L, 2 & 5 terminals all connected together]

 

[Robin Engelbertink]

Can you not see the 'Your Media' folder with my 2 pictures in it? How can I attach a picture to make it easier for you
Thanks again, you are so helpful!

 

[Robin Engelbertink]

HONEYWELL HW Controller

• Robin Engelbertink
• 27 Nov 2017

 

[Robin Engelbertink]

I might have confused you when mentioning 'immersion heaters'. What I meant to say was: I have 2 large hot water cylinders. These store hot water for the showers and hot water from the tabs in the house.
In case the boiler breaks down or there's no gas, I can turn on the electric immersion heaters so it heats up the water in the cylinders. I have actually never used them but I think this is the idea.

Yes, the Honeywell is wired to the boiler. The only think the Honeywell is used for is telling the boiler to heat water from 6am-10am and 8pm-10pm daily for the cylinders.

Can you see my pictures now? A picture of the Old Nest and Honeywell controller.

I get your point regarding no need to add another L and another N from the Honeywell to the L and N from the old Nest to the new Nest As long as one not feeds of the other).

So it seems VERY EASY!

 

[stem]

Thanks for the photos, and clarification.

Yes, simply swap the the CH wiring from your old Nest and connect in exactly the same way to the new Nest as you described "N, L, 2 to L and 3"

I can't see if there is just a grey wire, or a grey and black wires in terminal (4) of the Honeywell, but whatever wires go there now, need to go to the New Heatlink terminal (6) 'Hot Water Call for heat'.

No other wires need to be transferred. they can be disconnected and removed. It might be easier to remove the whole cable and install a new one with just the core(s) you need.

Finally the Heatlink Live needs linking to terminal (5)

 

[Robin Engelbertink]

I'm the one that needs to thank you! I'll report back once I've done the upgrade so others can benefit from your knowledge as well.
Just to clarify: Yes, there is a GRAY and BLACK wire in terminal (4) of the Honeywell.

Final Question - in case the boiler breaks down or there is no supply of gas, can I then manually switch on the immersion heaters so they heat up the water in the cylinders?

The Heatlink is connected to the boiler only so I guess sending a signal to the boiler is not a problem?

 

[stem]

Yes, there is a GRAY and BLACK wire in terminal (4) of the Honeywell.

That's probably because you have two hot water cylinders, and the original installer ran a separate wire to each.

in case the boiler breaks down or there is no supply of gas, can I then manually switch on the immersion heaters so they heat up the water in the cylinders??

Yes, that's what they are there for. Leave them switched off if you are using the boiler to heat to heat the water, they cost about 3 times as much to run.