Vaillant inbuilt monitoring vs MID meters

Correct, Vaillant’s figures will only include the outdoor unit, however assuming there is no secondary pump inside the house the Vaillant indoor controller a tiny amount of power, the biggest consumer is the 9W to open the 3-port valve during DHW, about 9Wh per day! It’s so tiny it can be discounted. Most installs will have the indoor controller connected via a FCU to the main heat pump supply so will be included in 3rd party monitoring.

Monitoring the indoor controller is more significant on other models of heat pumps which have the primary circulator pump inside the house powered by the indoor controller, or the system has multiple pumps.


@glyn.hudson @Zarch Thank you both for the detailed explanation. Much appreciated.

Using Emoncms - graph to compare daily deltas for the ‘electricity_Energy’ kWh figure against those shown in the MyVailant app.

15/12 | 13.2 | 12.9
16/12 | 6.9 | 7.2
17/12 | 5.6 | 5.9
18/12 | 4.6 | 4.8
19/12 | 6.0 | 6.2

I couldn’t spot anywhere to set timezone in MyVaillant app. Perhaps it just uses the address specified in account settings.

Is “Earned Environment Energy” the heat the ASHP has extracted from the air?

Sounds like another term for energy yield (from the Vaillant docs)


I have a freshly installed Arotherm plus 105/6 with a VWZ MEH 97/6 hydraulic station and did quite some investigations regarding the built-in monitoring that I would like to share. First some notes on my hardware setup:

I am reading the eBUS data using ebusd and an Esera USB ebus coupler (eBus Heizung Koppler & Gateways) plugged into a Raspberry Pi using this csv config to decode the data: eigene CSV erstellen und einbinden · john30/ebusd · Discussion #720 · GitHub. It is then being sent to my MQTT broker. I am polling the following measurements every 10 seconds:

ebusd/hmu/CurrentYieldPower - Current vaillant “Environmental yield” power
ebusd/hmu/CurrentConsumedPower - Current electrical power
ebusd/hmu/WaterThroughput - Water flow rate
ebusd/hmu/FlowTemp - Flow temperature
ebusd/hmu/ReturnTemp - Return temperature

I am also measuring the electrical power using a Shelly Pro 3EM; albeit this is for the whole installation. I also installed external temperature sensors on the flow and return pipes (PT100 + MAX31865, manually calibrated in a water bath between 0-100°C to yield zero relative temperature difference).

Using the eBUS values for flow rate, flow and return temperature I calculate the heat power. I also calculate this using the reported flow rate and my own external temperature probes. The eBus queried values (i.e. provided by Vaillant) are piped into emoncms: Emoncms - app view

Here are my observations:

  1. Vaillant reported electrical power very closely matches my Shelly measurements. As the power by Vaillant is reported in kW with only 0.1kW increments, I’m using my shelly data instead.

  2. The Vaillant “Environmental Yield” power very closely matches the result I get when I calculate heat power using flow rate and (flow-return) temperature and then subtracting electrical power. Most likely this is exactly what they are doing internally. Here’s a graph showing the Shelly electrical measurement (P_el,shelly), reported Yield power (P_yield,hmu), my own calculated heat power (P_heat) and the sum of yield + electrical power. It matches exteremely well. Integrating this yield power over the day gives almost exactly the same value as the Vaillant reported environmental yield energy that can be read off the VWZ device display.

  1. The graph shows a segment at the end of a heating cycle where we can see behaviour between on- and off state of the heat pump compressor. You will notice that electrical power and yield power drop to essentially zero, but my own calculated heat power does not. Why is that? - That’s because even when the heat pump is off there is a reported deltaT between flow and return of about 1.2K. This should not be there as there is no power input to the system. Flow and return should be at the same temperature and slowly decay at the same rate. As a matter of fact, my own temperature probe measurements show exactly this, as can be seen in the following graph. Where my own PT100 flow + return measurements drop to the same level when the compressor is off (and this temperature closely aligns with the Vaillant reported value), the Vaillant reported flow temperature stays around 1.2K above the return temperature. As a matter of fact, this offset is also visible during operation when the Vaillant flow temperature reports around 1.2K above my own measurement. I do trust my own probes more since what they are measuring makes sense from a physics perspective; and the return measurements exactly align with Vaillants measurement.

This 1.2K difference coupled with my 1600 l/h flow rate translates to a whopping 2.2 kW overestimation of heating power by Vaillant, which in turn results in a much overreported environmental yield and exaggerated COP.

Further evidence for overestimation of heat power:

We recently had a -10°C average day and I had a flow temperature at around 35°C (hooray for 140mm fans under the radiators!). According to the Vaillant specs, I should get a COP of around 3. The measured COP is 4 - which while I would really like but won’t believe for one second. The same figure is reported by the myVaillant app.

Furthermore I know the heat power requirements of my house very well. In preparation for the heat pump installation I monitored gas consumption using an impulse counter last year and correlated gas usage with outdoor temperature. Over the last heating season I found that I need 3.75 kWh per day for every Kelvin difference between inside temperature (20°C) and outside temperature - and that was with an inefficient 30-year old gas heating system. Using Vaillants reported heat power measures I get nowhere close to that but always significantly higher. I would expect something lower since I’m at much lower flow temperatures, the system is better insulated and does not dump a lot of heat into smoke and my heating room. For the aforementioned -10°C day, I’m getting 4 kWh / K based on the Vaillant data - which is too high. I have essentially never seen a value < 4 kWh/K which I find highly suspect and which led me down this rabbit hole in the first place.

This is either a defect on my pump - which can be fixed as it is still under warranty, or a systematic way to overinflate COP measurements…(of course the app states that the reported values are calculated and can be significantly off).

My question is: Can anyone confirm this behaviour? Are your reported flow and return temperatures also significantly apart even when the compressor is off? How well do they match your own measurements?


Thats really interesting @Andre_K, thankyou for sharing this. Can you see the flow and return temperature sensors used by the Vaillant? What does the contact with the pipe look like? Are there pockets or soldered copper sleeves? It’s very easy to introduce this kind of error with surface attachment of temperature sensors rather than pockets if not done well… though this does seem like a quality control issue that could be easy for vaillant to fix given that these are sensors inside the outside unit…

@glyn.hudson it would be great to get this running on the system that you installed!

I unfortunately don’t know what the sensors look like and won’t currently open the outside unit to check. I will bring it up with my installer & Vaillant service and update here if anything gets fixed. In case they do open the unit I will definitely peek over their shoulder.

It should be very easily detectable in quality control given that it is a very simple check of flow vs return when the compressor is off.

I wonder how this impacts general operation of the unit as the measurement of flow temperature influences the energy integral and probably also informs power modulation.

Using ebus it’s a 0.5 degree delta for me. I did notice this and only calculate heat if delta > 1.5.
It’s hard for me to compare heat generated vs when we had gas as the building has increased in size and I don’t know the efficiency of the old gas boiler. But ASHP heat is in same sort of range as previous gas kWh.

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Flow/Return in August. Often the return is warmer than the flow !

Interesting results. 0.5 °C is better than in my >1 °C but still too much in my opinion, especially since (at least for me) the return temperature is spot on.

2 posts were split to a new topic: Integrating MyVaillant app with EmonCMS

My installer wasn’t very helpful and I’ll launch an inquiry with Vaillant. Some more things I found:

From a service manual, it appears the sensors are extrnal to the pipes (13 and 19):

Also, it appears the return temperature also slightly varies with outside temperature (higher than my inside measurements when it’s warmer outside). I have implemented a simple running fix in Home Assistant:

  1. Calculate the delta T between flow and return
  2. When the pump is idle (i.e. in case it’s cycling), take the Flow-Return delta at 10 minutes after it got idle and store this as an offset to subtract this number from the flow temperature. This will give a running calibration of the delta T to be zero in the idle phase as would be expected.
  3. Use the corrected flow temperature for power calculation.

Apparently, the electricity measurement in Vaillant HPs is MID approved:

The inbuilt meter is being used for the OVO Heat Pump Plus trail for billing purposes via the Vaillant Internet gateway.

The heat output measuring is not MID approved, it seems to be the temperature sensing is where the greatest error and variability is found.


Good to know at least the electricity meter is accurate. Even with my corrections above the measured temperatures seem to be dependent on outdoor temperature and whether the pump is heating or making hot water. I ordered high accuracy pipe sensors and will fit them on the pipes entering the house but use the built -in flow metering for calculating a more accurate heat estimate. I have DS18B20 sensors there now and they do an OK job and match up with PT100s further down the line at the hydraulic station outlet, but the new pipe sensors will be a further improvement I assume.



Following the exchange between @dfeist , @Zarch and me in the Vaillant owners Thread, here’s some comparison data:

My system

Roughly a 1.2K constant offset between flow & return. This massively overstates heat generated in the Vaillant stats. My own (non MID, but properly calibrated together in an ice bath & sous vide) sensors work as expected.

@dfeist system

A 0.3K offset between flow & return but in the opposite direction than for my system, leading to an underestimation of delivered heat and thus COP. Heatmeter sensors work fine as flow&return are identical between cycles.


@Zarch system

Difference between Heat Meter and Ebus

  • Flow: around 0.3 & 0.4
  • Return: around 0.4 & 0.5

This would work out to a constant delta of around 0.1-0.2. Just from eyeballing it appears Vaillant would also slightly underestimate here.


If anyone else wants to contribute a similar graph I’d be happy to add it to the post.

@Zarch , @dfeist : If you don’t mind - could you also provide a snapshot of how flow rate compares for reference?


My Sontex flow rate is under-reporting due to dirt. Once I get it cleaned during service (in a couple of weeks), I’ll upload a comparison.

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Delta T pretty close here. Only my DS18B20 sensors cannot measure the DHW runs. Since they are external to the heatpump and the DHW cylinder is inside the heatpump.

I taped them with copper tape to the copper pipes and then wrapped them in Neoprene tape. All pipes are also sleeved with Neoprene.


Very interesting. Do the absolute temperatures also agree or only the deltas? Did you calibate the DS18B20 in any way?