It is most of the above. The back plate that holds the pipework connection can resonate, and the pipework inside can resonate, so you have to wedge the plate and strap the pipes inside. On top of that, compressor noise alone can be very loud, louder than my customers are willing to accept. (it wakes them up with levels of noise).
Fan is fine - no noise here at all.
I didnāt mention the noise, but yes there is quite serious noise from the compressor when running at full speed! Same observation on my unit that the fan is very quiet, but the compressor is noisy and since most of the noise comes out of the back of the unit I was considering noise a absorbing panel on the house wall behind the unit to stop the reflected noise. I just about have room while still leaving 25cm gap. Thanks for the note on the resonating. I will also look into treating that at source.
@UrbanPlumber Have you spoken to Vaillant about the issues? I wonder whether they would at least do something about the noise issue under warranty. And at least have some position on the under-power issues.
Just a small data point: our 7kW Arotherm unit does not exhibit excess noise when running flat-out. The compressor is audible outside, but far from egregious. Totally silent indoors.
It sounds like the noisy units have bits/pipes rattling around and resonating inside the chassis, which is a rectifiable defect rather than a chronic design flaw.
I think it gets louder once it ices up, at least thatās the case for my 10 kW unit. The air flow is much louder when the air is forced through the ice build up. Still not terrible but noticable outside.
Just to follow up on my 7kW Arotherm compressor noise. In my case, there is resonance somewhere in the compressor assembly at medium to high speeds. I am speaking to the installer, but it seems like a Vaillant warranty issue to me. I canāt stop the vibration or determine exactly where it is - my best guess is that it is in the compressor mountings, based on some probing.
The screenshot below shows the audio spectrum from my phone microphone on the landing near the cupboard with the hot water cylinder and the bottom half shows the peak matches the compressor speed.
Sounds like thereās something resonating in there, or a faulty/prematurely worn compressor. Definitely not normal! Could also be the compressor decoupling mounts becoming degraded and unduly hardening in cold weather.
My 7kW unit sounds nothing like this.
Get it checked out under warranty.
Does anyone have a video of how a compressor should sound like when running at maybe 50-80rps?
It would be interesting to hear. I have only heard mine and only considered that there might be a problem when winter came and it was frequently running at high compressor speeds. From listening to mine and observing the vibrations at different speeds, I would guess that it is normal at 50rps (start of the video) and only becomes abnormal when parts of the assembly start resonating at higher frequencies (at the point where you hear the ātickingā). Obviously it all sounds louder with the side of the unit removed.
Iām watching this thread with interest.
Our 7kW unit sounded like a tractor in the recent cold snap and barely mananged to get to 40 degrees when it was 0 outside. It was running flat out in between defrosts every 35-45 minutes for long periods. Our heat loss is 7.5kW at -2 so that seems to track really closely with the numbers above. Most of the house did get to 21 eventually but it felt touch and go.
Our design flow temp is 45 at -2, I donāt think thereās a chance our unit could reach that.
Thanks @willjuk all sounds very consistent with above, strange about the noise issue! would be interested to hear if anyone gets to the bottom of why that is?
Funnily enough @TrystanLea, Vaillant are visiting tomorrow to look at the issue. Iāll report back.
Vaillant visited regarding in my 7kW compressor noise issues yesterday (see Vaillant Arotherm Owners Thread - #764 by Plug1 which is a follow-up to my previous post on this thread). I will be interested to hear how you get on 
So the engineer came this morning. At full power the unit sounded fine, though not a surprise as itās 7 degrees here today. He measured the sound levels, it was all within specs so he didnāt do anything at all. Pretty annoying.
Iāve just ordered my own sound meter so I can record evidence next time it happens and call them out again.
An easy way to spin up the compressor is by setting the hot water mode to āNormalā (no compressor throttling), then triggering a hot water reheat cycle. The service engineer should have known how to make the compressor run full tilt regardlessā¦
I would try this myself, then get the engineer back.
Do you hear the same qualitative differences in the noise as the compressor speed increases as I observed (see previously linked video). I.e., distinct evidence of vibration/ resonance. The Vaillant engineer did improve this, as I commented, but I was not convinced he treated the root cause (and even now, I think I hear some deterioration). As Andre suggested, I am going to follow up with Vaillant again. My next step will be to try and speak to someone at Vaillant who can give a definitive answer on whether the type of noise, as well as the loudness is something that is normal (as I really donāt think it is).
I ramped up the set temperature and the heat curve. It was drawing 3.4kW, which as far as I know is full whack.
Could you detail exactly what the engineer did to improve your unit? Specifically, where the tape/foam/whatever was applied?
Yes, I will take photos when I get chance, but I am becoming less convinced as time goes on that it helped much. He basically put several pieces of foam tape around the bottom of the compressor.
Hi everyone, just to add a similar experience to this thread. 7kW Arotherm+ in its second winter. Iāve always found quite a lot of compressor hum is transmitted to the building pipework, which is faintly audible in every room at higher compressor speeds. We donāt use the bedroom closest to where the external pipework enters the building for sleeping, but I could see it being a problem if future owners did. Outdoors, the compressor gets somewhat noisy at high speeds, to the point that I think noise reduction mode is necessary overnight to avoid annoying neighbours.
In the recent cold snap I noticed resonant buzzing develop which elevated noise levels from ānot silent but okā to āmaking a racketā, even at the compressor speeds which noise reduction mode limits it to. This seemed like a justifiable warranty call out issue, if I can replicate the noise in front of them.
Now that the weather has turned milder, I havenāt noticed the resonant rattles, even with the odd defrost still occurring. I did notice that pressing on the little plate where the water pipes come out of the outdoor unit seemed to muffle a lot of the buzz.
Similar to Grahamās video, I took off a side panel to see if I could find anything obviously loose, and I couldnāt believe the amount of noise coming from the compressor. The panel has thick foam blocks on the inside which clearly does a lot of muffling. I thought I saw the compressor visibly vibrating quite significantly like a washing machine on a spin cycle, but Iād want to have another look to be sure.
Posting today on Facebook showing pipes can move in the hole in that plate creating a rattle. Maybe small changes in size with lower temperature have someone do to with noise problems
