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.

31 votes

Active · Last Updated


  • AGray333

    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!


  • jelly
    jelly ✭✭

    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


  • oldIron
    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).
  • Mattc

    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

  • Abh

    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!


  • brianacox

    I've got a related problem, which I'm going round and round in circles with......I've had a Tado for a number of years (upgraded it too). We've got a Gledhill water store, which is heated by an oil boiler and two immersion heaters (using both solar and cheap overnight electricity)

    I suspect that I need the system reconfigured/re-wired to operate as two distinct elements, so that:

    Hot water – where the Tado hot water schedule (when the water needs heating) just starts up our oil boiler, and heats up the water in the water store. There is a pump associated with this moving water from the boiler to the waterstore (and back)

    Heating – where the Tado heating schedule (when any TRV or the room thermostat needs heat ) starts up the pump (a second one) associated with the radiators.

    At the moment the heating side (if heat is required) also tells the oil boiler to start up. Clearly it only does this when the water store isn’t up to temperate BUT I don’t want to do it at all.

    The reason, as I mentioned, is that I’ve got two alternative sources of heat for the water store, 1) being solar electricity (excess electricity using an immersun diverter) being fed into the two immersion heaters (alternately) on the water store, 2) off peak cheap electricity between 00:30 and 04:30 which I can automatically (using the immersun) to start up the two immersion heaters, i.e. 2 immersion heaters x 3 kw x 4 hours = 24 kw of heating potential.

    So at night, I will set the Tado Hot water to finish at say 8.00pm, but the heating to finish at 10.00pm. Because the house is warm at that time, and the water store hot at 8pm… there should be enough hot water to continue to heat the house until 10pm…. The water store will then be much cooler and with 350 litres of water there will be plenty of heat capacity for the cheap electricity to fully deploy.

    Is this possible? how do I do it? (my 'cheap electricity' won't be around many more months, but I would still like to have a distinct separation between, 1) heating water, 2) heating the house. Whatever I do to separate the two (I've just gone back to gravity fed rather than pump fed TADO settings), the water is heated (by the oil boiler) when the rad pump turns on.

  • I have a fully pumped system with a separate hot water cylinder with a cylinder stat. How can I get Tado to control the water temp of my boiler