Altech thermostat to Nest

[Billwarbero]

Hi,
I would like to challenge myself with the installation of a Nest thermostat to replace an old and partially faulty Altech wireless.
I have no prior experience in this type of job and I am wondering whether it's a good idea or not, but if I don't try I will never learn.

The Altech is currently wired via a Honeywell junction box. (Images attached) Can I leave the J box in place and just replace the receiver with the heatlink?

Many thanks in advance

Bill

 

[stem]

You don't give us much to go on there. Assuming that you have a combi boiler and not a boiler hooked up to a separate hot water cylinder, then yes you can simply replace the Altech with a Nest. As you don't say which model of Nest, I will give you the instructions for Nest-e which is the easiest for DIY installation.

The Altech connections are as shown below:

The wires that are in the Altech NO and COM go to the Nest-e terminals shown below with wires connected to them that are also marked NO and C (COM) Simples!

As Nest-e is battery powered, the wires presently in Altech L and N are not required anymore and can be either isolated, insulated and tucked safely out of the way. Or, disconnected and removed completely.

If there is a separate timeswitch or programmer elsewhere currently controlling the heating, then that will need to be set to be permanently 'on' to stop it interfering with the operation of the Nest.

The cable shouldn't just be left hanging loose, it should be secured or contained in trunking to prevent it being inadvertently pulled out of the terminals. It's currently a very poor quality installation.

If you want to use a different version of Nest, or have a system with stored hot water (aka hot water cylinder). Then things will be different. If this is the case, please post back.

 

[Billwarbero]

Thanks for the prompt reply, and sorry for the scarcity of information.
The boiler is indeed a Vaillant combi.
The Nest is a 3rd gen, so yea, as you say, slightly different, and will need powered.

I've attached another image of the J box as previous one was blurry.

Thank in advance.

 

[stem]

In that case, it's just a matter of moving the wires over exactly as they are, from the Altech to the Nest Heat link. The terminals have the same names on the two devices.

Altech L = Nest L

Altech N = Nest N

Altech COM = Nest (2) 'Heating Common'

Altech NO = Nest (3) 'Heating Call-for-Heat' Normally Open (or NO)

You can use a separate plug in power supply for the Nest thermostat, or alternatively connect it back to Heat link terminals T1 & T2. If you do wire the thermostat back to the Heat link, it will also require and earth connection making to the terminal adjacent to T1 & T2

 

[Billwarbero]

Many thanks, will give it a go later and report back!

 

[Billwarbero]

hi again
so I went back to the shop and swapped the NEst 3rd gen for a Nest-e as it seemed easier to install.
Removed L and N that were left dangling from the Altech, connected NO and COM to the Nest, and then I went back to turn the mains on and the boiler now doesn't turn back on...

I've pulled out and rewired the coppers in the junction box in case there was a loose connection somewhere, but no joy. The boiler seems dead...

I had disconnected the Altech earlier, before connecting the Nest, and hot water and everything was still working fine. The boiler only stopped working after I plugged the wires back into the Nest.
I have tried to disconnect the Nest but the boiler remains dead.

Any ideas?

 

[CBW]

Ian it’s possible you’ve removed the L and N for the boiler? (The dangly bits)

 

[Billwarbero]

No it was definitely the L / N going into the Altech.
The power is still connected between the junction box and the boiler (see photo)

 

[CBW]

Where does it take its power from? A spur? Is that on? have you checked for 230vac?

 

[Billwarbero]

I don't think so. There's no fused switch for the junction box or the boiler. I isolated the mains from the fuse box.
The mains connection appear from the back of the J box coming out of the wall. (Attached photo)

 

[CBW]

There must be something, somewhere, as it’s 3 core flex coming out of the wall into JB then from that to the boiler. I doubt 3 core will be going to the consumer unit.

 

[Billwarbero]

Nothing I can see or that I'm aware of the whole time I've lived here, apart from the fuse box switch (that isolates all the wall plugs in the boiler room, not just the boiler).
Sorry

 

[muggles]

Are there any other cables running into your boiler, besides the 3 core flex we see in the photo? Presumably there were two before you started? What happened to the second one?

 

[CBW]

Double check your wiring, I’ve highlighted in a red square, only the earth wire is showing copper strands, so you may have crimped onto the neutral insulation.

Are there any other cables running into your boiler, besides the 3 core flex we see in the photo? Presumably there were two before you started? What happened to the second one?

I think he’s removed them as there were another set of wires, but for the old thermostat.

 

[Billwarbero]

Are there any other cables running into your boiler, besides the 3 core flex we see in the photo? Presumably there were two before you started? What happened to the second one?

Yes, the NO+COM cables still dangling out of the boiler. I've disconnected them from the Nest for the time being.