Nest 3rd Gen Thermostat - Replace Undefloor Heating Thermostat

[tododo]

Hi all

I bought a Nest thermostat for the single zone underfloor heating we have

We have an existing thermostat for the undefloor and the plan was to just replace that with the nest just to control the underfloor heating

I have another nest wired up to the boiler and that works really well - heatlink etc all good

My idea was to just replace the thermostat for the underfloor heating
However im not sure if Ive made a mistake though as there are only two wires on the back of the nest and the one we have now has four

So it maybe that Ive jumped the gun here and I might have to re-sell

Can anybody help
Thanks

 

[tododo]

I think this is the spec sheet of the existing thermostat

Heatmiser Slimline Datasheet (radicalheatingsolutions.co.uk)

 

[ericmark]

there are only two wires on the back of the nest

I count 13 terminals. T1 and T2 connect to the control sensing device. That device does have two connections

but it is part of the whole unit. There is a USA version

it may be called Nest Gen3 but it is very different.

 

[Taylortwocities]

@tododo please specify exactly which Nest thermostat you have.

your existing thermostat has three wires and an earth. If your new stat only has two wires (I assume it’s battery powered) you only need to connect the live (brown) and call for heat (black) wires. The grey is the neutral. Put that in a bit of insulated terminal block it isn’t needed. Ditto for the earth wire. Put that in a separate bit of terminal block.

 

[tododo]

Yes T1 and T2 are on the back of the nest itself. I have since read I need to have a separate Heatlink for each zone too. I didnt know that - so will need to take a look at that junction box where the existing thermostat is terminated. Its not as simple as I originally thought though.

Its a nest 3rd gen - not the E model

Google Nest Learning Thermostat 3rd Generation, Stainless Steel - Smart Thermostat - A Brighter Way To Save Energy : Amazon.co.uk: DIY & Tools