Can I use the extension kit as a hot water controller? New house and confused.

Hi, apologies if this is a question that gets asked a lot but i have recently moved house and the setup is different. I have been using Tado in my last house for the last 6 years successfully but need a bit of clarification for what to do.

My previous house was gas central heating with a danfoss programmer wired directly into the boiler and connected to a thermostat located in the hallway. When I replaced the danfoss with the Tado I had the tado extension kit replacing the original programmer wired directly to the boiler which connected to a tado wireless thermostat in my hallway which controlled my central heating and hot water. 

My new house is Oil central heating but with no programmer at the boiler. Instead I now have 2 zones of heating (ground floor and 1st floor) with a Honeywell CM707 programmer at each location and a separate programmer for hot water control in the airing cupboard (Honeywell ST9100c).

I will need to buy a new thermostat to cover my second zone but was wondering if you could give me advice on if i can use the extension kit i already have to replace the hot water programmer. It doesnt need to have a thermostat as the hot water control only needs a simple on/off signal. Could you please clarify if this is correct and if i can configure the 2 thermostats to be central heating only and the extension kit to be hot water only or if I need to approach this differently.

If this is possible could you also please provide advice on how the wiring would need to be implemented.

Photos attached of the current configuration.



  • You need two wired thermostats to replace the CM707s, that's the easy bit. The extension kit will directly replace the ST9100C for hot water control, BUT you may still need the wireless temperature sensor. Even though you won't be using the CH channel on the receiver I'm fairly sure it will not operate without the temperature sensor. One reason for having the temperature sensor is to provide a physical device for turning the HW on/off.

    Someone on the forum might have the complete answer, or you'll have to ask customer support directly. Whatever the outcome, I'd be interested to know if the sensor is required.

  • @GrilledCheese2

    It does work without the wireless temperature sensor for the extension kit, thats the way I use my setup and it works fine. I think that before the extension kit was changed to the wireless reciever you could purchase a kit from Tado that contained a wired thermostat and an extension kit all together. I'm not sure if the same applies to the Wireless Receiver though but I think it should.

  • Thank you both. Yes that was the kit I purchased with the wired thermostat and extension kit, although i only had to wire the extension kit at the time and have the thermostat communicate wirelessly.

    I have had a reply from Tado support as well to confirm the extension kit should work as hot water control only so in theory all i need to do is purchase another thermostat for my second zone and i'll be set.

    I'll update once I have it up and running.

    Thanks again.

  • Kashx81
    edited April 18

    Can you please share the wiring of STC9100C and Tado hot water control wiring. I find the Tado app instructions let you down during the installation (like they did on my replacement of CH Honeywell T3) .

    I have a similar system, replaced the zone1 and 2 thermostats with wired Tado thermostats and now want to replace my STC9100C hot water controller with the Tado programmer that came in the wireless V3+ kit.

    Thanks alot for your help

  • Tado support helped a lot with my setup. The installation instructions via the app don’t acknowledge this type of setup but they do have a pdf which they can send you which gives the instructions you will need. I can’t upload the pdf myself but if you email [email protected] and ask for “BU4.1 - Honeywell ST9100A - ST9100C - Hot Water - Single Channel - Bridge present - ENG.pdf” that should work (assuming your setup is the same as mine). Once you get everything wired in you will also need to ask them to set your programmer as your hot water control remotely as the app doesn’t recognise it as a controller by default.
  • Ah figured out how to upload the pdf. I should stress however that this was for my setup and it might not be the same as yours so you would be better to explain your situation to tado support just in case

  • Thanks i will contact Tado support. I was not aware they have to remotely set my programmer to hot water control