What wiring are my thermostats using?

[HenryGregory]

Hi there,
I have two thermostats, one on the ground floor and one on the first floor. They go back to my Baxi combi boiler.
As such, I only need smart thermostats that control the heating as there is no need for hot water control with the boiler being a combi.

This is the wiring behind my existing thermostat:

The existing thermostats are using the black and brown wires. The blue wire is terminated with a plastic connector. The blue wire does not connect to the existing thermostat, only the black and brown wires.
The grey wire is disconnected and doesn't plug into the thermostat.

This is what the back of the thermostat looks like, note it runs on batteries:

Above the boiler, there is this connector box. I can see that for both zones (first floor and ground floor) the black, brown and blue wires are connected along with the earth. The grey ones are not connected.

I am not sure if this setup is using a modular or relay style of connection. Can anyone help?
I have been considering getting a Tado Wired Thermostat V3. I understand it has a built in battery much like my existing thermostat. Does anyone know if this would work ok with my current wiring?

Thanks in advance.

 

[CBW]

No, they’re not relays, just mains switching. The thermostats when calling for heat, make the switch close, sending mains voltage to the corresponding zone valve, which in turn motors open, closes another switch which then sends the signal on voltage to your boiler. The batteries power the front of the thermostat for the display. You need x2 thermostats if you are wanting to keep the 2 zones. Tado should work, iirc, they’re volt free, which means they send whichever voltage is applied to them.

 

[HenryGregory]

No, they’re not relays, just mains switching. The thermostats when calling for heat, make the switch close, sending mains voltage to the corresponding zone valve, which in turn motors open, closes another switch which then sends the signal on voltage to your boiler. The batteries power the front of the thermostat for the display. You need x2 thermostats if you are wanting to keep the 2 zones. Tado should work, iirc, they’re volt free, which means they send whichever voltage is applied to them.

Thank you for the fast reply and clarification.
Was thinking of doing one zone for now and see how it goes. I have the Tado Air Conditioning Thermostat for my study and it works quite well. I have been wanting to put in Smart Thermostats for ages but they are a lot of money when you only use them maybe 5-6 months of the year but now I have Tado already installed for the air conditioning, I might as well continue using it so thought maybe start with the downstairs zone and if it works well, get another without the hub connector for zone 2.

Thanks again for your help.