The MyVaillant App: a review

Friends, regular readers will know that I love my heat pump, a Vaillant Arotherm plus model with a nominal maximum heating power of 5 kW.

But regular readers will also know that I have been very disappointed with the software and controls for the heat pump. Back in October 2022 I wrote:

Vaillant Arotherm Plus Heat Pump: The good, the bad and the ugly.

In that article the “good” referred to the mechanical and electrical operation of the heat pump; the “bad” referred to the mysterious absence of a user manual; and the “ugly” referred to the VaillantsensoApp‘ used to control a few of the functions.

Recently Vaillant have released a new MyVaillant app to replace the sensoApp and I was eager to try out it. Could it be the elegant swan that grew up from the ugly duckling of the sensoApp.

In case you don’t have time to read this finely-crafted article, here is a summary of my findings: the MyVaillant app is a big improvement, but the operational data it provides is – as best I can tell – still just as inaccurate as it was previously.


After logging on initially I was mildly impressed, but then the next time I opened the app, I was asked me to log on again: select my country location, e-mail and password. This has happened several times since and I have been told over that Vaillant are working on this. I won’t mention it again, but it is a sign of poor testing.

After eventually logging on one is faced with a pleasing simple ‘Home Screen’. A glowing green circle displays the current set point temperature with the actual temperature below it – these numbers change in increments of 0.5 °C. The glowing circle changes colour from time to time, but I have no idea why!

Plus and minus buttons allow the set point to be easily adjusted. Clicking on these brings up a dialogue box which asks how long to change the set point for. After the chosen period – default is 3 hours – the set point will return to it’s previous setting or programmed value.

Click on image for a larger version. The Home Screen of the MyVaillant App.

The Home Screen contains buttons which link to four more important screens.

Click on image for a larger version. The Home Screen of the MyVaillant App and the screens to which it links directly.

These screens (see-above) allow access to the basic controls. It’s nice to see that ‘Activate Hot Water Boost’ – the most common reason I need the app – is just one touch away from the Home Screen.

Perhaps the most important screens are those for planning the weekly cycles for (a) heating and (b) domestic hot water. These are – in my opinion – textbook good design.

Click on image for a larger version. The screens for adding an  additional regular period of domestic hot water heating. Notice that one days settings can be copied and pasted onto another day.

So the app is well-structured, pleasant to look at and easy to use. A big improvement.

System Performance

Even bigger improvements have been made to the screens showing the system performance. An example screen is shown below for the week beginning 23 January 2023.

Click on image for a larger version. Example page show energy information for the heat pump during the week beginning 23 January 2023.The screen is shown left and on the right the screen is annotated to show how the various quantities relate to one another.

The display page shows:

  • A: The electrical energy used to operate the heat pump – in this case 125.9 kWh
  • B: The thermal energy captured from the air – in this case 230.1 kWh
  • C: The thermal energy delivered to heat the house – in this case 332.1 kWh
  • D: The thermal energy delivered to heat hot water – in this case 23.9 kWh

From these quantities the app calculates the Coefficient of Performance (COP) which it calls as Energy Efficiency.

If one touches any of the small graphs, a more detailed version is shown.

Click on image for a larger version. Clicking on the small energy graphs shows more detailed versions.

This display structure has been well thought through and is well executed. I would wish that the data could be downloaded, but this presentation is basically excellent.

However sadly the performance data shown is not accurate.


The MyVaillant app warns people that it is not accurate. But I think that despite this warning, in the absence of any other information, most people will take these figures at face value.

Click on image for a larger version. This warning screen appears before one sees the energy information pages. I recommend that one does not click the box asking not to show the message again. This should remind one that the data can be significantly in error.

Please note: Energy consumptions, energy yields and efficiencies are extrapolated based on various parameters. The actual figures may differ substantially in some cases.

Fortunately I have a monitoring system which measures the electrical consumption by the heat pump and the heat output of the heat pump. This allows a direct comparison between the app’s estimates and a measurement system which is certified to be suitable for billing.

So for the week illustrated in the figures above, the actual figures are shown in the table below.

Click on image for a larger version. Table showing the MyVaillant App estimates for electricity consumed and heat produced together with the measurements of these quantities by billing-grade instruments.

The MyVaillant estimates are seriously in error.

  • The estimate of the electricity consumed is in error by 9.3%.
  • The estimate of the heat produced is in error by 22%

Consequently, the estimate of the COP is seriously in error.

For the week in question, the average temperature was 4.0 °C and the minimum temperature was -5.1 °C, a cold week by London standards. A COP of 3.3 in such a week is quite respectable. A COP of 2.8 is not so great, and might lead someone to search for system improvements which would be illusory.

Click on image for a larger version. Temperatures in my back garden during the week in question.

The real problem with these errors is that the erroneous estimates are completely plausible.


Assuming that Vaillant sort out the problem logging on to their app, then this app represents a really significant improvement over their previous offering. To all the engineers who have worked on this I would like to say: Thank you.

But the inaccuracy of the reported quantities is significant and I feel that if Vaillant cannot improve these estimates, then they should be indelibly marked as ‘indicative’.

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9 Responses to “The MyVaillant App: a review”

  1. Rob Fee Says:

    I am concerned now as we are about to have the same make heat pump installed.
    PS did you get octopus sorted?

    • protonsforbreakfast Says:

      Rob, Good Morning.

      Firstly, yes, Octopus sorted out the bill straight away – and also the bills of many other people who were affected.

      Regarding heat pumps, The Arotherm plus itself is first class: I don’t think there is a better one available – although there are many that are perfectly fine. And none of the heat pumps incorporate accurate monitoring for reasons of cost. So if you want to monitor the system and really know then you might consider installing a heat meter similar to the Sontex 449 I used and separate power meter for the heat pump installation. You will need to read these (say) weekly or additionally buy a monitoring system – a data logger – such as that sold by Open Energy Monitor.

      I would recommend getting someone who knows about the system to install it.

      Best wishes


      • Roaming Rob Says:

        Good Morning Michael

        Thank you for the positive reply, I have tried to make changes for good, for the grandchildren, having spent years driving diesel cars for hundreds of thousands of miles. So with limited resources we have over the last 3 years gradually installed solar PV, a home Battery, changed from Gas cooking to electric and changed the diesel to BEV (and it is wonderful, car mad unfortunately all my life) we are now about to make the biggest change to an A2W heat pump and we are very afraid, it’s the unknown!

        But, I won’t hold you to account for being so persuasive, I will just thank you for the little bit you have helped us to change and so help our grandchildren’s future. So Thank You.

        Love your utube.


      • protonsforbreakfast Says:


        First of all congratulations on teh changes you have made so far:I am really happy that you like your EV: appreciating that a ‘green’ change can make things actually better AND greener is a shocking, but true.

        Regarding your Heat Pump, I hope your installation goes well. Please let me know how it goes. There are probably not too many more really cold days this winter but I wish you lots of solar-powered hot water through the summer and a snug winter in 23/24.


      • Roaming Rob Says:

        Thank you Michael

        You are a genuine Guy.

        May I ask if you are booked for any presentations this coming year?


      • protonsforbreakfast Says:

        Rob, thank you for your kind words.

        Your request prompted me to make a web page for the blog listing my forthcoming talks:

        So thank you! If you have a local group and planets align correctly e.g. not too far and I happen to be free, I would be happy to talk to any local groups of which you are a member.

        All the best


      • Roaming Rob Says:

        Thank you that’s brilliant

        Many thanks


  2. Rob Cannell Says:

    I would be interested to know how Vaillant calculate their CoP. If they were using a flow meter and temperature sensors it ought to be very accurate. Since temperature sensors are cheap and flow sensors expensive might they be using something else (e.g. circulating pump parameters) as a proxy for flow rate?

    • protonsforbreakfast Says:

      Rob, I think you are right. The warning as one enters the energy page says as much

      “Please note: Energy consumptions, energy yields and efficiencies are extrapolated based on various parameters. The actual figures may differ substantially in some cases”

      So I think that as you say they may use pump speed or power as a proxy for flow rate and this is likely the origin of the discrepancy.

      Thank you for pointing that out.


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