You can also use quiet more which reduces the compressor by 30%, which would take you from 120rps->90rps.
So is Vaillant reducing the compressor RPS in line with the reduced pump speed configured? Does it do the same for heating? It would be weird if it did for heating given “auto” doesn’t adjust the flow rate down when the ASHP modulates down.
Set-back is one option. But a better option IMO is to set the quiet mode to be active from 18-20hr. This will limit the compressor which in turn limits the current. I think I already answered this question, and gave current values for noise reduction %'s numbers on FB, right?
I’ve finally gotten around to starting to monitor our Arotherm+ 7kW this weekend (it was installed back in March/April).
Overnight (when colder) the runs look fine - at least an hour runtime per cycle, very smooth and with good COP.
Today as things have warmed up to 10C-12C outside I get a strange dip in the flow temp and heat output on each (short) cycle - but during the dip the electricity input does not also reduce.
Has anyone seen this before?
The unit is mostly running at minimum heat output (~3kW) even overnight wheh the temp was 6.5/7C.
Common Arotherm behaviour, nothing to worry about. Take a look at most of the Arotherm on the heatpumpmon list. 
5.5 COP at 10C outside on a 7kW is just about on spec, so system looks to be working well. 
Thanks Mick - well I won’t worry about it then but I do wonder what it’s doing!
John Cantor was observing this same phenomenon on his Mitsubishi…
It’s something to do with the “compressor discharge temperature” and where the evaporation happens.
Here’s a chart i’ve pulled together from the Vaillant Czech sheet.
This simple graph shows the COP you should expect to achieve at various outside temps.
As you can see, my 5kW model can’t reach the same COP heights as the larger models.
I’ve finally made peace with this fact now.
Using the Heat Pump app I think it makes it easy to see if your installation is hitting expected outputs?
Just pull out a heat run at one of the outside temps from the graph and match up the outputs?
COP 5.27 on heatpump app versus 5.1 from the Czech spec. So that’s good.
Same here, 4.6 from both.
Mick,
Something caught my eye on this graph. The graph is based on 35/30; at 0C outside it claims 3.8kW max output for 5kW unit. This seemed low to me from what I remember so I went back to the table on your blog from the Vaillant brochure which has the various outputs and COPs crossed referenced with outside temp and flow temps, and there it says 6.9kW for same outside and flow temps. Which one is correct?!
Cheers,
Tom
Ah wait the graph from the Czech sheet is for COP, even thought the title says its for KW output?
Yeah, I ballsed up on the titles, sorry. good spot, i’ve updated.
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
