Vaillant Arotherm Firmware 351.06.07 Problems (Energy Integral)

In the main Arotherm thread we have briefly talked about the double counting bug affecting firmware revision 351.06.07 on Vaillant Arotherm heat pumps.

In an attempt to summarise the whole issue, @dfeist and I have co-written an article over on my Energy Stats website to do just that.

It will be interesting to hear what version of firmware people are running and whether you are experiencing more cycling than you expect.

Good info to know about you system would be

  • Arotherm Model (3.5, 5, 7, 10 or 12)
  • Firmware Version
  • Pre-Install Heat Loss: kW
  • Measured Heat Loss post install: kW
  • System Volume: Total litres in UFH, Rads, Pipework, Buffers / Volumisers
  • Compressor Hours
  • Compressor Starts
  • Average cycles per hour (Compressors Starts / Compressors Hours)
  • What outside temp your system goes from constant steady state running to cycling

Hope you find this article useful.


My answers

  • Arotherm Model - 5kW
  • Firmware Version - 351.06.07
  • Pre-Install Heat Loss: 5.2kW
  • Measured Heat Loss post install: 4.2kW
  • System Volume: approx 100L (rads / pipes only)
  • Compressor Hours - 7194
  • Compressor Starts - 9292
  • Average cycles per hour - 9292 / 7194 = 1.29
  • What outside temp your system goes from constant steady state running to cycling - around 7C

Yes, my system is definitely affected by the firmware bug!


Too soon for me to have some of the details but -

  • Arotherm Model - 12kW
  • Firmware Version - 351.09.01
  • Pre-Install Heat Loss: 10 kW (my estimate, formal estimate higher)

Ran -60 and -100 settings on consecutive nights. Currently with a desired temp of 19C on Expanded (as don’t really want it on in the day and cba with programming the weekly timer etc)

Dropped to 2 noticeably longer cycles with longer intervals despite nominally lower outdoor temp (6.4C!) which suggests it is working correctly. Yet to be awake and at home whilst its running to watch the energy integral move.

Interestingly day 1 the pump ran between cycles, day 2 it didn’t (which I imagine is just expanded kicking in as it definitely felt cosy last night!)

Another interesting observation (from my point of view) is 5.5 kW is the output it was giving me when the compressor backed off which is a little higher than I had hoped for given I suspect the unit is oversized for my needs.

Thanks for sharing.

  • Arotherm Model - 5kW
  • Firmware Version - 351.09.01 (installed mid-Dec 2023)
  • Pre-Install Heat Loss: 3.43kW
  • Measured Heat Loss post install: TBC
  • System Volume: TBC
  • Compressor Hours - TBC
  • Compressor Starts - TBC
  • Average cycles per hour - TBC

(data from HA integration on 1st May, cycles per house 1,592 / 1,617 = 0.98)

Will add the other info ASAP.

Emoncms - app view

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Hi Mick,

Thanks very much for sharing this. I’ve been surprised by the amount of cycling our Vaillant has been doing, so when I read your article I felt a sense of dread, sure enough I’ve got the dodgy firmware.

Our ASHP was installed in Jan 2024 but was manufactured in November 22 - we’ve had several faults with it. Vaillant say there shouldn’t be more than 6m between manufacture and install date.

Speaking to technical suppor today, they’ve denied it’s a fault, but did identify my gas pressure was low, so they’re sending an engineer out. This is the second gas leak our unit has had, in 4 months. :frowning:

Arotherm Model (3.5, 5, 7, 10 or 12) - 7
Firmware Version - 351.06.07
Pre-Install Heat Loss: 6 kW
Measured Heat Loss post install: - not sure how I calculate this?
System Volume: Not sure - 4 bed house, 100mm centres UFH downstairs, rads upstairs, all open loop.
Compressor Hours 1671
Compressor Starts 1472
Average cycles per hour (Compressors Starts / Compressors Hours) - 1.13
What outside temp your system goes from constant steady state running to cycling - 7C
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Thanks for taking the time to produce the superb blog Mick.
I have gone through exactly the same journey and am currently in the same position with Vaillant customer support.
It is a real shame that Vaillant are unwilling to accept their responsibility for this. It is going to lead to premature failures of heat pumps, due to excessive cycling and provide more reasons for people not to move to heat pumps.

My heat pump was installed in Feb 2023
My figures are

  • Arotherm Model - 10kW
  • Firmware Version - 351.06.07
  • Pre-Install Heat Loss: 8.2kW
  • Measured Heat Loss post install: 6kW
  • System Volume: approx 130L (rads / pipes only)
  • Compressor Hours - 2701
  • Compressor Starts - 5331
  • Average cycles per hour - 5331 / 2701 = 1.97
  • What outside temp your system goes from constant steady state running to cycling - around 3°C
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Nice piece of work documenting Vaillant’s immoral position on the firmware bug. Interesting that Vaillant apparently changed out the board free for some complainants, but not for most.

I had the board replaced on my 2022 Arotherm+ at the fixed price cost. You lose all the operational statistics and any settings related to the board (cooling, eco setting, etc). Also, as the SN of the external unit is coded onto the board somewhere, the original SN is lost. Consequently, the Vaillant app loses all past usage data, although it may exist on Vaillant servers somewhere. Vaillant are “aware” of this. I asked if the old SN could be written back to the board via ebus, but received no response. You’d have thought Vaillant would have an engineer’s tool that pulled all the historical operations data and SN off the old board (or Vaillant servers) and pushed it to the new, but they obviously didn’t think very much about this at design stage.

So I agree that the Vaillant hardware is stone age compared with most other firmware based systems. My vr720f started burning through a set of batteries per week (first set lasted two years), which the engineer who changed the board shrugged his shoulders about. Should have pushed it as this would have been covered by the fixed charge. Now it seems that Vaillant’s policy on controller replacements is scandalous too: you can’t replace a faulty vr720f without having to buy a kit including the radio receiver and a wireless external temperature sensor too. This is eco vandalism in my view!

The underlying design of these components says something about Vaillant’s mentality as I see it: pretty hubristic to believe you are going to get firmware right and build products that will last indefinitely.

I will not be recommending Vaillant to anyone now!


Hi Jim,

Thanks for the reply and the details.
It’s sad to hear you’ve got the older firmware, but I think there has to come a point where original heat pump selection also comes into play with excessive cycling. Perhaps I need to update the article with that point.

With just a 6kW measured heat loss and a 10kW unit installed, there is always going to be early cycling at lower than expected temperatures. Yes, the newer firmware will help keep the on periods longer, but it can’t fix the big gap in the heat loss. If that makes sense?

With the 7kW model capable of going well beyond its 7kW badge, you could argue your installer could have gone for that, even with an 8.2kW loss? The 7kW can output 8kW at -2C, even at 55C flow. (9kW at -2C at 45C flow).

Thanks Mick
Agree with what you say but the MCS heat loss method is far from an exact science. I can see why installers err on the side of caution. The best source of quality data would be historical daily fuel usage (under design cold temperature conditions) but this was not available with a sight glass on an oil tank!
It’s looking like I’m stuck with a decision about spending another £500 to get the integral system working. Unfortunately Vaillant have yet to provide me data on what level of cycling the Arotherm is designed and tested against. In the absence of this type of information it’s a gut feel decision!

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Really fustrating that you had to pay for this. Have you seen improvements in cycling and efficiency?

Couple of other questions:

  • Do you think the vr720f battery issue is related to the firmware upgrade? Mine seems fine.
  • Was it just your external board that got switched out? Some people on German forums talked about needing to change internal board to. In my case only external board was switched out.

VR720f seems unrelated as the unit ripped through a set of batteries in a week prior to the board change. I’m going back to hardwired VR720.
Not tested the new board on heating: I really should do that!

Edit: now tested and energy integral is behaving as expected (live monitor updates every 30 secs by half the difference between desired and actual flow temp: ebusd off until controller issue sorted!)
00 351.06.05
01 351.06.06
02 360.02.02
01 351.09.02
After board change

Was cycling down to about -2C before. Will be interesting to see the behaviour next heating season.


My VR720f battery lasted almost 2yrs. Maybe to do with signal strengh or if dispaly is always on or brightness.

That will likely be same, just cycles should be longer. And if you can set min integral to -100 instead of -60 (without house temp varying too much), they’ll be even longer.

My first set too. Signal strength is 9 and the display is off. Still pulls 8mA in this state (40mA when active) so something has gone wrong on the board I think.

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I had read about the integral setting prior to buying my Vaillant 75/5 Split, on

I bumped it to 100 from the default of 60 during the winter and noticed a huge difference. I have before vs after charts. Will share them later.