Launch an external temperature sensor for the Smart Radiator Thermostats

I'm very happy with Tado overall, apart from the performance of the Tado Smart Radiator Thermostats. I’m finding that due to the way the Tado Smart Radiator Thermostats work, they heat up a room very, very slowly, and sometimes fail to get a room anywhere near the desired temperature. I've noticed that after they turn on the radiator, they seem to then quickly turn it off as it thinks it’s reached the target temperature, when in fact it hasn’t and it's just due to the proximity of the temperature sensor to the hot radiator.

I performed a test with the bedroom in our house, it’s a simple rectangular room, measuring about 3 x 3.5 meters with a single radiator. The doors and windows were kept closed throughout:

The room was at 19ºC at 11:30 am and I set Tado to heat it to 22ºC.

The radiator heats up, but the SRT temperature sensor quite quickly reads 22ºC so Tado turns the radiator off. However, the room is actually only at 19.5ºC (measured on a 2nd thermometer elsewhere in the room), right next to the radiator it is 22ºC but not elsewhere in the room.

You then have to wait for the temperature by the radiator to cool down (about 30 mins), before the radiator will eventually heat up again, but then the whole cycle starts over again with the radiator quickly shutting off.

This means it takes a very long time for the room to get to the target temperature (and sometimes not at all), as the radiator keeps getting turned off before the room temperature is anywhere near the target temperature.

After 6.5 hours the room had still not reached its target temperature of 22ºC and is only at 20.5ºC at 6 pm, because Tado kept prematurely turning off the radiator.

Please see this graph:

Which shows the 22ºC target temp in green, the actual room temperature (measured by another thermometer at another point in the room) in orange, and the Tado graph showing it constantly turning the radiator off.

You can see from the graph that this isn’t simply solvable by setting a “Temperature Offset” in the app, as when the radiator isn’t warm the Tado thermometer more accurately represents the room temperature (and is often actually under-reporting it, not over).

However, to see what would happen, I went ahead and set an offset. As the Tado was effectively over-reading the temperature by about 1.5ºC, I set an offset of -2ºC. I then left it for over 2 hours to settle, and this was the result:

As you can see, an initial boost helps gradually raise the actual room temperature, but as it still quickly turns off the radiator, the actual room temperature only reaches about 21.3ºC, still not even close to the 22ºC target.

A side effect of this offset was that the next morning, when the radiator had been off overnight, Tado thought the room was at 16ºC when it was actually at 19ºC, and caused it to needlessly turn on the radiator. So as you can see adding an offset doesn’t solve the issue and actually introduces more problems.

In my opinion, the SRTs need to be much, much cleverer, learning the characteristics of the room and then ignoring any initial overshoot in temperature to allow the actual room temperature to get to the correct level.

Either that or Tado need release a small, cheap (~£30) temperature sensor that can be placed in the room away from the radiator to give much better results. I know you can use a Tado Smart Thermostat, but at £100 these are too expensive to put in every room.

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  • mw9342mw9342 ✭✭✭


  • +1 - the Smart Thermostat is too expensive to use for this role, and there are rooms where I would never want to have a display or control interface (kids bedrooms!)

    A simple remote temperature sensor at a reasonable price would be great.

  • +1 - external temperature sensor would be ideal.

    We have odd shaped rooms with varying temperature profiles.

    It would be better for us to have a sensor near where we need it and slave it to the TRV.

    Ideally the room would either average between the TRV and the remote or use the remote sensor.

  • edited February 27


    This is exactly what is causing me to put off buying Smart Radiator Thermostats. I had wondered about the sense in placing a thermostat so near to a radiator (let's be clear, nobody recommends placing a room thermostat near a radiator) and I have heard tales like this elsewhere.

  • Hey guys, I’ve been having the same problems as you have described in one of my bedrooms.

    Been experimenting over the last few weeks with various things as it’s been driving me mad as to why the TRV was calling for heat so often, now I think I’ve found a solution as results look very promising, at least for me anyway.

    The room in question is a small box room 3.3 x 2.4m with a single panel rad 600 x 900mm.
    The TRV is (was) fittted vertically with a -3 deg off set to achieve required temp on the other side of the room, measured using an electronic weather station remote senor that has only a 0.3 deg difference to the TRV.

    Today I turned the valve and TRV so it’s horizontal, what a difference this has made.
    Off set from TRV removed, temp even across the room and boiler on a lot less often.

    I would show you screen shots of the graphs but at the moment I can’t copy them to this thread.

    Hope this helps.
  • jcwackyjcwacky ✭✭✭

    @MarkC That's a good tip (if you're in the position to be able to change the valve that is). I too noticed that even moving the TRV a small distance from the radiator had large improvements. I think it also varies on your radiator type. If you have a new one, with the side panels, even these can help stop some of the heat coming out sideways towards the TRV. I was going to experiment with adding a small reflective panel between the TRV and radiator.

  • I like the idea of a cheap room stat, I would buy them if reasonably priced. I have 11 x TRVs and would like to add perhaps 3 cheap stats for the most used rooms.

  • +1 for this....

    I work in the HVAC industry and wouldn’t ever dream of placing a temp probe right next to your heat source.

    I’m having the same problem and this solution would fix the issue. No way am I going to spend another £99 on a smart thermostat when I’ve already spent £59 on a ‘smart’ radiator stat.

  • I think 2 point calibration for the temperature offset might help here - an offset at high end to ensure the room reaches the target temperature and an offset at the low end to prevent premature turn on

  • @GJWalsh started this thread requesting 2-point calibration. @jcwacky, I suggest you have a look because it would circumvent the unwanted consequence of setting a large offset that you both have experienceed:

    "A side effect of this offset was that the next morning, when the radiator had been off overnight, Tado thought the room was at 16ºC when it was actually at 19ºC, and caused it to needlessly turn on the radiator. So as you can see adding an offset doesn’t solve the issue and actually introduces more problems"

  • Absolutely +1

    I also reported it to customer support and they told me to purchase a thermostat for each room. It's crazy but is the only way at the moment, so +1 also for GJWalsh.

  • Without wishing to confuse, I’d also suggest the algorithm should take into account measured temperatures from all/multiple smart radiator thermostats in a zone. Different radiators will warm up a different rates and this may enable the system to learn better and “balance” the heat output across the zone to avoid hot/cold spots. Throw the data into an AI engine!
  • I've also got this problem on vertical valves - it does not affect my horizontal valves. I've got a vertical in my bedroom and typically I hear it come on, and within 5-10 mins it goes off again... The radiator is barely warm and it's gone off because its been influenced by heat from pipe / near radiator edge. I've currently got a sock wrapped around it to try and stop this!

    Suggest "damping" the reading somewhat after calling for heat as currently its not handled well. Of course trying to isolate the temp sensor from the radiant / conducted heat would help, but will never be the whole solution.

    Perhaps allow setting a deliberate "overshoot" so heating comes on at set point, but doesn't go off until set point + overshoot. Not ideal, but easy to do in software.

    A cheap external sensor would also be useful approach, but think software fixes most applicable to greatest number of users.
  • What about an external (wired) cheap temperature sensor to be connected to the smart trv?
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