@jamespa Thanks James. I’ve requested a call out from Vaillant, via my installer, and provided a recording of the sound and meter reading. I also have external temperature and humidity readings for the time it occurred which will hopefully give them some context  

The noise level was out of the ordinary, even for a very cold week. The vast majority of the time our pump is very quiet.  It was interesting to read Urban Plumber’s posting, referenced earlier in this topic, where he raises his concerns over recent noise levels from Vaillant 7kw units such as mine. It does suggest there is some sort of issue specific to this unit. 

Overall we’re really happy with the performance of our heat pump and were impressed by how well it worked down to -6 in the cold snap. Hopefully Vaillant can get to the bottom of what’s causing this problem. 

Good.  Please post any outcome and be persistent with Vaillant.  I think you may have a particular problem, but even the 'commonly reported' increase in compressor noise above 80% somewhat spoils, to my mind, this otherwise almost perfect pump.  

The Vaillant product manager has contacted me about 8 times in the three months since I first used their 'find an installer' service, so I get the impression that they are still interested in collecting feedback from users in the UK.  This being the case its important to give it!

I very rarely hear my 7kW Arotherm+ but have twice heard it roar at the end of the defrosting cycle when it's blown out a cloud of fog. It's fitted under one corner of the kitchen window and I need to be in the right place at the right time to see and hear what's happening. The unit is mounted on what looks like a big concrete slab which is actually a piece of expanded polystyrene sprayed with some cement and faces out into the garden so there's no risk of reflected sound.

Posted by: @tallmarc

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...  It was interesting to read Urban Plumber’s posting, referenced earlier in this topic, where he raises his concerns over recent noise levels from Vaillant 7kw units such as mine. It does suggest there is some sort of issue specific to this unit. 

... 

I had a Heat Geek engineer around yesterday who was vacillating between a 10kW Vaillant Arotherm Plus and a 7kW, the reason being that the 7kW has a software problem at the moment and there are reports of it not working so well at colder temperatures - he didn't mention noise though.  Specifically he referenced models produced since November and perhaps it was related to a specific batch.  Anyway Vaillant are investigating.

Please be nice: He was a good chap, knew what he was talking about, and I can't remember exactly what he said, nor was he overstating the problem.  He wasn't dissing the product or Vaillant it was just that the calculated heat loss, a smidgen over 8kW, was on the boundary for a 7kW or 10kW.  His preference was for the 7kW because the air change value used in the heat loss calculation is a bit over-egged and using a more reasonable value brings it into 7kW territory.  However, given the software problem he was considering whether it might be prudent to go with the 10kW.

Interesting.

I must admit Id be very reluctant to get a different model to the one I need because of a known software problem, assuming Vaillant admit to it and are fixing it.  Id probably rather delay a while or, if its patchable over the air, install anyway and wait for the patch. 

That said I have been told (but not verified) that the firmware in the ODU is not patchable over the air.  Maybe some interrogation of your engineer is warranted, or indeed direct to Vaillant, if he can give you some sort of reference.  I have found their tech support to be very helpful but of course it may be different if you are pressing them to fess up to a fault!  You could tell them that you would go with another make if they don't answer!

I wonder if I have the bug, mine was installed mid November.

The earliest it could start to be installed would be June!  I would hope it would be fixed by then or, prior to install start, to have the discussion again.

@jamespa ours (without a noise issue) was installed in September. I too recall reading the firmware is in a hardware (not-remote programmable) chip and changing meant a pcb change.

Just weighing in here after reading through. We've had our 5kW Aerotherm for a couple of weeks and it does have a very noticeable hum/buzz under all types of load. I've been on the Facebook forums for Vaillant Aerotherm and a few have reported the same tone. 

I've attached a video which you may be able to pick out the hum. No idea the specific cause or whether 'normal'.

Posted by: @samiebon1

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Just weighing in here after reading through. We've had our 5kW Aerotherm for a couple of weeks and it does have a very noticeable hum/buzz under all types of load. I've been on the Facebook forums for Vaillant Aerotherm and a few have reported the same tone. 

I've attached a video which you may be able to pick out the hum. No idea the specific cause or whether 'normal'.

I dont think you attached the video.

@jamespa

Forgot to press insert into post! Woops

I didn’t hear any problem with that noise it was less than walking on gravel. Have you another example recorded?

@samiebon1 I am no expert at all, but that is a bit of a penetrating tone & sounds like a unit that is on a defrost cycle or hot water cycle in V cold weather. At the same volume as a steamy boiler gush, that would have a much greater capacity for nuisance. Difficult to gauge properly and relative noise levels as videos with phones are notoriously awful in terms of noise - noise reduction and quality of microphones interferes significantly with the true picture. 

I was reading this today, headlined "myths and misinformation" - one of the "myths" is always claimed to be noise. Experts warn 'myths and misinformation' about installing heat pumps in homes persist - Mirror Online

Quite astounded with the headline (and the abuse of the term myth) & how it will rally those who say heat pump noise is never an issue... given that within the article a Dr. Balaam being interviewed about his unit states quite clearly: "...it’s noisy"!

Hope it is a distinct issue of something gone a bit wrong in this case and that you can get it sorted.