Installing Extension Kit with Hot Water Cylinder

Hello, as the Tado chat is pretty much not responding and they closed their phone lines, I am hoping someone here can help.

We have a Vaillant UniStor unvented hot water cylinder and a Vaillant EcoTec plus 618 condensing boiler. There is a Honeywell ST9400C control for hot water and heat next to the hot water tank. Furthermore there is a wireless room thermostat I want to replace with the Tado Room Thermostat. I have fitted each radiator with a Tado smart thermostat.

I now want to install the Extension kit to the boiler, and install the Tado Room thermostat. However, I think I prefer not to mess with the Honeywell control for the Hot Water and leave it to control the Hot Water as I see no specific benefit to having Tado control Hot Water and don't want to mess with that system.

How do I get the Extension Kit NOT to control the hot water? And how do I set the Honeywell for the Heat once Tado Extension kit is fitted - just to CONTINUOUS heat?

Many thanks!


  • Hi there

    Did you ever get an answer to your question on this? I have the same scenario (different boiler and cylinder but same scenario) and trying to figure out how to install everything so that I don't mess up the hot water.

    If you could point me in the right direction that would be awesome.

    Many thanks.

  • Hello - yes it is working great. The HEAT setting is CONTINUOUS on the Honeywell control, and heat is controlled by the Tado Extension kit. Hot water is still controlled by the Honeywell and not by Tado - I cannot exactly remember how it went, but the set-up in the end was very intuitive - I think you just click NO at one point in the set-up process, or you only select heat.