Hot water temperature monitor via extension kit

My heating system is the hot water storage type where a larger tank is used to store hot water for heating the radiators and hot water supplied via a heat exchanger. The tank is heated by a solar panel on the roof and a wood burning stove. Backup heating is via a gas boiler, which is controlled by Tado. It would be good if the temperature of my hot water tank could be monitored via the extension box and the temperature could be used to control the boiler, rather than the simple hot water on/off.

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  • Hello Jelly,

    I had the very same issue of not being able to control the temperature of my hot water tank (I don't have solar or wood burner additions). I solved this with some simple and cheap 3rd party electronics. I purchased a SONOFF TH10 from amazon (£17). My tank has an old electric element fitted which isn't used, I removed only the thermostat from here and inserted the temperature probe for the TH10 (You could cut away some of the insulation and tuck the sensor in next to the tank instead). Give your TH10 some main power and access to your wifi. (It uses an app called eWelink, it's not the best but does the job). Now the clever part, setup your auto on and off temperatures in the eWelink app, I chose minimum 66 and max 73. Once this is done, download and sign up to the IFTTT app, it's well intergrated with many apps but importantly its will be able to link eWelink and Tado. Create two applets one which commands your Tado to "Return to automatic Control" when the TH10 is OFF (Below 66). Another for "Turn hot water off" when the TH10 is ON (Above 73). This means that I can use my tado schedule as normal, including the location services. While the hot water is active in my schedule the boiler will fire up until it hits 74 and then cut out until the tank drops back below 66.

    Sorry for the long post, fire me any questions if you have any.

    Good luck!


  • Hi Andrew,

    Many thanks for your reply. This seems like a good solution to the problem and I like the way you linked the Tado and the eWelink. This also looks like a much cheaper solution than a Tado device. At the price I think I’ll get one, may be two as I could use it to hand over control to Tado when the solar panel output drops below a set temperature. I see you can also link these to Arduinos so that opens up more possibilities.

    Thanks again for the great idea.

    Kind regards


  • At present we can only see whether hot water demand is on (water cold) or demand is off (water hot). Please could we have actual temperature from a tank sensor - so a box similar to a Tado room stat that either mounts directly on the tank or has a short wire to a sensor. The app would then show the water temperature (again similar to room thermostat).
  • agree a proper hot water tank sensor to feed in , could indicate temp , not just off on , could allert low temp

    im sure cost savings could nee made controlling hot wTer tank better not just off on timer , seem so a bit crude compared to the room temp controllers

  • I've installed a new Viessman system boiler and water cylinder connected to Tado via Extension kit over Opentherm and was pretty disappointed to find the only benefit was to set DHW temp from app or smart thermostat. Given the thermostat in the cylinder is low voltage back to the boiler, why can't the extension kit report current DHW cylinder temps and therefore manage DHW heating more efficiently. Tado doesn't provide any way to monitor how long or when the boiler needs to heat water for the cylinder. Would be great to see current DHW temps and request a boost via the app especially when the kids are all running showers/baths etc!!

    For those with DHW OT setups, adding that level of intelligence to match the reporting/features that smart room thermostats offer would improve DHW heating efficiency. Appears to be a big hole in Tado functionality when compared to the options/intelligence for room heating.

    As Andrew Gray mentions above, maybe the solution for older, non-OT DHW measured cylinders, is to replace on/off cylinder thermostats with a smart Tado DHW thermostat providing Tado another revenue stream and customers the DHW control missing currently.

    thx in advance!