Underfloor heating replace optimum duostat with Nest

[leroyjenkins]

We have a wet UFH system in our kitchen that was installed with an Optimum thermostat. All working fine but I’ve bought a Nest to replace it, as this is what we’re using for the central heating in the rest of the house, and is much easier to use.
(After this replacement we’ll have two nest thermostats and two nest heatlinks).

I was hoping that replacing the optimum duostat receiver with the Nest heat link would be quite straightforward, as it would just be a case of switching some wires over. But having opened the current box, it all looks a bit chaotic to me. I’m wondering if anyone can give me a bit of a steer as to what might be involved.

You can see here our UFH pump and the cable going to the Optimum duostat receiver (top left). There’s another cable coming from a 230V Honeywell junction box. So I assumed cable from pump is the call to heat and the other is the power.


For reference, this diagram from the manufacturers website shows what should go where…


And here’s my installation. It’s difficult to get the full setup of the wiring in a photo, this is the best I could do…


From what I can see. There’s two wires coming from my pump, a blue one that’s been put into slot 3, and a brown into slot 1.
Then from my power cable, there’s a black wire going into 1, a grey wire going into 3, and a brown wire going into 4.
Then it also looks like there’s a wire going from 4 directly to 2.
And also a earth wire from both pump and power cable going nowhere (taped up in the photo).

Is this some kind of crazy mess that will take a proper electrician to sort out? Or is there a straightforward way to rewire this all into the Nest heat link?

Many thanks

 

[CBW]

It’s the T1 and T2 you’ll struggle with, unless you’re going to use the USB? L and N are straightforward, looks like the Com and NO are easy enough too, being numbers 2 and 3 on heat link respectively.

 

[leroyjenkins]

Thanks. Yep plan on using usb to power to the nest stat.

So that does sound quite straightforward.
What I don’t understand is why there’s a wire from my UFH pump gong into the 3rd neutral slot, and not the 2nd COM slot.

 

[CBW]

If it’s going to neutral, perhaps they just needed a neutral supply from somewhere and took it from there?

 

[leroyjenkins]

Looking at it a bit more, my issue is that my mains cable comes with 4 wires (black, grey, brown and earth), there does not appear to be a neutral.
So I'm unsure about how this is supposed to go into the Nest heatlink.

Think I may have to contact an electrician.

 

[CBW]

Likely the grey has been used as a neutral, this is common practice, if they did it correctly it would be sleeved blue.

 

[ianmcd]

Looking at it a bit more, my issue is that my mains cable comes with 4 wires (black, grey, brown and earth), there does not appear to be a neutral.
So I'm unsure about how this is supposed to go into the Nest heatlink.

Think I may have to contact an electrician.

the colours dont mean anything