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.