Looking at the Vaillant graph. If my heat loss estimate is 3.5kW, does that (optimistically) mean at -2°C the 5kW Arotherm would be using approximately 950W to generate the required heat energy?
Or are the COP figures based on heat energy coming out of the heat pump and I need to allow for losses throughout the system?
If you system IS capable of 3.7 COP at -2C… but remember this chart is at 35 flow. So it’s better suited to higher outside temp comparisons. ie, many people will be 35/30 at 7C and above
You’d have to have a large amount of rads/UFH and insulation to be capable of 35C at -2C i’d suggest?
The 45C flow / 40C return chart (from the Czech charts) shows around COP 2.8 at -2C.
Hope that makes sense?
I got 2.5 COP at -3C last winter.
Hello, does anyone know the official line from Vaillant on frost protection valves? Just in the process of installing a 5K Arotherm plus, and going this route rather than gycol but has anyone had any issues with warranty etc? I also noticed in Urban Plumber’s latest videos, he only fits one (to the return). I have two ready to go, but if one is sufficient that would be less to go wrong, less heat loss etc. Look forward to getting up and running and joining in on the detailed performance analysis!
I don’t think Vaillant mind what you use, but any damage due to freezing would not be covered under warranty. I recently fitted a Vaillant with a single AF valve. I think using one is fine, it will be able to relieve the pressure on the system. Depending on the installation location It’s debatable if any are needed, oil boilers have been fitted outside for decades without the use of glycol or AF valves, it’s very unlikely to be a problem. Using one AF value seems like a reasonable precaution to me.
Thanks Glyn, seeing as I’m on the south coast (and urban so low chance of prolonged power cut), I too was wondering if even necessary. I will go with just one - I know someone I can can give the other to who’s plumbers were about to add gycol! Does it matter if it goes on flow or return? Urban plumbers vids are on the return I think, so will go with that…
Here here!
Hello Guys.
my Vaillant 55/6 was just installed yesterday, and I am struggling somewhat with the settings (from the VRC720). The installer was not very familiar with Vaillant 
, and he did just the basics.
The overview: Vaillant 55/6, no buffer, only heating, 1 zone, all K33 radiators, 35mm primary pipe;
with the circulating pump at Auto setting, I am getting 850 l/h, but it stays at this level ALL the time !?
Insider temp 23C / outside temp 4C now;
Now, this is where I would ask for your help:
many thanks,
ADrian
Yes it does this, don’t worry. The Arotherm uses DT to modulate output
Time control
Deactivate. Not heard of anyone having any joy with this.
Not sure on this one.
Choose the heat curve to match your heat loss.
I wrote this article
Normal
I go with active (with room influence). Again, mentioned in the weather curve doc
So choose your setback temp, say 18C
Then in your timed programs, choose your target indoor temp, say 20C
04:00 - 22:00 - 20C
Then if you leave the rest of the day ‘blank’, setback at 18C will kick in and the heat pump will adjust the weather comp curve down to match.
With all the above settings, the only thing you’ll change is the heat curve.
If you’re too hot, turn the curve down.
If you’re too cold, turn the curve up.
Once you’ve changed the curve, give it a day to see how things settle.
Mick, really appreciate it ! thanks
This depends on your setup I think. I’m not a heating engineer, but we’ve just got this sorted after a very puzzling few weeks from installation, after the circulation pump turned out to be wired into the wrong output. (One of those “very simple in hindsight, but incredibly hard to diagnose with the information available” things.) I thought it worth posting just in case anyone else hit the same issue.
As far as I understand it, one’s system might have:
1. Only the pump inside the heat pump unit, in which case MO 2 / M1 is probably irrelevant. From your description of your system, this sounds like your situation, and I think you can probably set these both to “not connected”.
2. A secondary circulation pump for the heating. We have one installed post-buffer tank, which is wired into output MA1, and the HP control module config is set to “MO 2: Not connected” & “MI: 1 x circulation”. It (now!) comes on when the heating is on, and works in tandem with our two zone valves.
3. An optional secondary circulation pump for DHW, wired into output MA2. This is for those who want “instant” hot water badly enough to install a return loop in their hot water piping, and they can then use the DHW circulation pump schedule to control when it circulates.
Our problem was that the heating circulation pump was wired into MA2, and was being controlled by the default settings in the DHW schedule. So our system effectively responded perfectly during the day, and ignored all inputs at nighttime, because the pump was switching off, and at night the HP was merrily topping up the buffer tank instead of the house! Bamboozled us, our (otherwise very competent) installer, and Vaillant, as the symptoms were sending us chasing after app and control unit firmware red herrings. I allowed myself a smug/wry smile when I managed at last to diagnose it 
Cheers,
Jo
I’m curious to know other Arotherm owner’s experience of defrost cycles and the effect on COP in recent days. I’ve been watching my stats and my COP really takes a beating during the defrost itself (obviously), but also during normal operation between defrost cycles as it gradually ices up and efficiency drops. I’m seeing defrosts about every 45 minutes at current RH levels (sorry don’t have an outside humidity sensor to give a value on it). My flow temps are very modest, currently between 28-32C, so this seemed like quite a frequent defrost regime to me.
My other observation is that during DHW runs, there is no defrost cycle. Is this intentional by Vaillant to just to hell with efficiency, let it frost up but just get the DHW cycle completed. My DHW run last night was 3 hours long at significantly higher flow temp than heating (obviously) and was not interrupted by a defrost cycle.
Cheers,
Tom
https://emoncms.org/app/view?name=MyHeatpump&readkey=1548bb92f8413211bb7c36cfa154ac94
Interesting. What kind of cylinder have you got? That’s not a DHW profile I’ve seen before, running at maximum temperature instead of ramping up like Mick’s perfect example.
Mixergy using tip coil. It’s an interim fix up before I get PHE
Mine certainly does defrost during DHW.
Maybe it’s just the way you are caning at with 65C flow!! 
Around freezing and high humidity does have a big impact. This is my 7kW Arotherm+ last night, freezing fog and around -2C.
Another question for Arotherm+ owners - how noisy is your unit when running hard?
Ours is really quite noisy - low but very audible and annoying buzzing noise that carries through the house. I assume that’s not normal?
On ours, yes the noise ramps up. I noticed a buzzing that on closer inspection is just the case (maybe a screw or something), as it went away when I pressed on it
Our ecodan took 90 minutes for a 170L DHW cycle at -1°c here last night. I wish its controller was a bit smarter at waiting in terrible but improving late evening weather.
For those of you that use/monitor “Working Figure” on your Arotherm installs. The heatpump controller DOES know about month boundaries. It must get it from the sensocomfort?
You can see here where I’ve recorded monthly heating working figure via the ebus in to
Home Assistant. It flips instantly on midnight into the new month and starts a new calculation.
I assumed the controller was a bit dumb and did a rolling 30 days or something. But the evidence suggests otherwise.
So bear that in mind when looking at ‘month’ working figures.
Yes, can be. Mine starts off quiet, then as it ramps up it goes through a noisey spoy. Then when it gets closer to maximum speed it quietens down though can still here a slight hum. Then get the same going back the way as it cyclez off. I’ve got a 7kW Arotherm Plus. Has the reciprocating compressor. Would be interested to hear from those with the 12kW with the scroll compressor. From my time working with HVAC scrolls are quite quiet.
