Installing Tado Wireless Thermostat into a 2-zone heating system

Hi all,

I have searched through the forums to see if a previous post exists regarding my set-up, but to no avail. Apologies in advance if I have missed it though!

I recently purchased a Tado Smart Thermostat Starter Kit V3 and am looking at the option of self-installing this but I was hoping for some advice on the best way to achieve this.

My Current Set Up is as follows:

Boiler: Valliant Home Combi 35 (no separate hot water cylinder)

Thermostat: 2 x Honeywell CM907 Thermostats, one currently located on the Ground Floor hallway (wired) and the second in the master bedroom, again wired. Each thermostat is linked to a zone valve so we have two heating zones

Wiring Box: Danfoss WB12, the thermostat cabling, zone valves and boiler wiring are hooked up to this wiring box in the airing cupboard.

Desired Set-Up

I wish to replace my downstairs thermostat with the Tado wireless thermostat to control the downstairs zone. At this moment in time, I wish to retain the upstairs CM907 and eventually replace this with a wired Tado thermostat to control the upstairs zone.

In saying this, I am happy to temporarily compromise and run the whole system off the wireless thermostat and override the zone valves if needed.

I was hoping if anyone could provide advice on the best way to install this. I have attached photos of the wiring of the WB12.

Many thanks in advance.


  • The colours of the wires on the lower row are the guide to figure out what is going on. They go to the zone valves. The key wires appear to be brown on the lower row and black on the upper row, 7 and 8. The black wires probably come from the thermostats to tell the zone valves to open (Motor L) on the lower brown wires. The two orange wires on 12 are the valve AUX switch OUT that send Live to the boiler.

    With Tado, the wireless receiver will 'call for heat' (instead of your old room stat) from the zone valve. Work out which of the brown wires goes to your downstairs valve. You'll take out the black wire on 7 or 8, and terminate it safely on 9. The wireless receiver will need to powered from your WB12. On the receiver, link L to CH COM; and connect CH NO from the wireless receiver to 7 or 8. With an Earth, thats a length of 4-core cable. If in doubt seek help from a competent professional.

  • Hi Wateroakley.

    Thanks for getting back to me with your opinion - it is much clearer.

    Regarding the last sentence about earthing, is it possible to explain further, as I am not sure what you mean about the length of cable, and where the cable should terminate?

    Cheers and Best wishes

  • The length of cable ... to connect from the WB1 box to where you propose to mount the wireless receiver. Always run a cable with enough individual wires, plus an earth wire. Live Neutral Earth CH NO and a spare (for the HW channel?). So, four-core (or five-core) cable from the WB1 to the wireless receiver*. Pick up the L N Earth from the terminals inside the WB1 and on the wireless reeiver, terminate the earth on 'parking'. The fourth wire is to connect 7 or 8 in the WB1 to CH NO on the receiver.

    * If you use a standard three-core cable for L N and CH ON, then you've got a Green/Yellow 'earth' wire with Live power on it. (Dangerous / Shudder).

    Personally, it's good to have the heating controls in an accessible and visible location. Our CH installer put the original Honeywell controls and wiring centre in the outside boiler cupboard. Easy to fit, but difficult for the user. Now, the Tado receiver is on the wall in the study. Easy to see when we're WFH or from the kitchen. For our rellie, I fitted the receiver discreetly in the boiler cupboard. Out of the way from the inquisitive children. If needed, opening the cupboard door is easy to see the active lights .

  • Thanks again for clarifying - must admit I was having a bit of brain fade.

    So am I right to assume with my 4-core cable I do as follows

    Connect the N to 3 on the W12 Block

    Connect the L to either 5 or 6 on the W12 Block

    Connect the E to either 1 or 2 on the W12 Block

    Connect CH NO to either block 7 or 8 depending on which is the downstairs zone?

    Thanks again!

  • Yes, that's how I read your wiring. CH NO: disconnect the black wire from 7 (or 8) and park it onto 9.

    Thinking aloud ... with a 5-core cable, you could wire the upstairs thermostat and valve through the Tado HW control on the wireless controller. That would give you Tado schedule timing of ON/OFF and geo-location control of the upstairs heating valve through HW on the App.

    Move upstairs black on W12 block 7 (or 8) to 10.

    Connect W12 block 10 to HW COM.

    Connect HW NO to W12 block 7 (or 8).

    Set the wireless controlller as not-combi.