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Octopus Cosy 12 Heat Pump Regret: Incredibly Loud, Poor Heating & Constant Hum - Help!

razz · 2026-01-11T11:11:13Z

Hello all,I'm new to the forum. Just had an octopus cosy 12 installed on Friday. Massively regret it already. It's incredibly loud, not looking very cheap, and doesn't heat the house very well. Inside the house there's a constant hum, be it the pump itself, the various pumps, volumizer etc. and the sound of rushing water in the pipes. Utterly tired and depressed.

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Hook

(@hook)

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29/01/2026 1:07 pm

if you are on Facebook there is a cosy Heatpump group.

A director frequents the group and is quite active, so will definitely react to reports of noisy 12s.

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Mars

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29/01/2026 1:40 pm

@dedwards all these new cases are a bit worrying, because in general outdoor units from most brands are now very quiet, so surprising to hear Octopus' are so noisy. I assume you've flagged this with Octopus Energy, and I'll be very interested to hear what they say.

I will also raise this with TJ from Octopus.

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swwils

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29/01/2026 2:40 pm

Would be interesting to see the case geometry on the 12.

I mean the fan at an angle and lack of legs always immediately jumped out as brave choices.

I wonder if any production variations with certain parts pushes the tolerance for noise out of acceptable regions.

It's worrying to see them saying it's normal, that's not going to improve anything for either side, ultimately even if it is normal you'll have created a heat pump detractor.

Why don't they just have a ninja team that goes and sorts the 1% with weird tricky noise issues without fuss? It's a classic scale problem; 1% of a million heat pumps is still 10,000 customers 😂.

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Hook

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29/01/2026 2:58 pm

I think the Cosy 9 and 12 have the same dimensions?

If so I’m guessing the fan has a higher rpm on the 12.

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Mars

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29/01/2026 3:44 pm

Do these units have feet or does the full base just sit on the ground?

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swwils

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29/01/2026 4:09 pm

@hook oh that's interesting. I'm sure it will be different somehow, maybe a completely different fan or any number of bits.

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swwils

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29/01/2026 4:11 pm

@editor here is mine during install. Don't under estimate the groundwork though, it's alot of gravel. Through bolted to slab. They also now have the leg kit available but I don't think it's a default.

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Mars

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29/01/2026 4:19 pm

@swwils so is the noise reverberations or the fan?

For all the faults and issues with our 18kW Global Energy Systems heat pump, the fan noise would never have been a problem for us. The unit is sited 20m from the house, but had it been closer that would never have been overly bothersome.

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swwils

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29/01/2026 4:23 pm

@editor on my case, I think it's the fan causing a reverberation.

In other people's, it could be the pump (unlikely) or the compressor causing a reverberation. Or maybe a combination of them all. It's such a weird thing to experience, even very tiny shifts the the source frequency can make a huge difference.

In some others, it may well be the fan itself causing an airborne noise, but id like to think that's almost impossible, unless something is broken.

So it's tricky to work out and quite unlucky if your effected.

I'm kind of inclined to make small demo soon if I get time. If anyone has a Bambu 3D printer that does the vibration compensation before every print it's a really great example of similar.

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Toodles

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29/01/2026 4:32 pm

@editor And warmed your drive nicely?

Toodles, heats his home with cold draughts and cooks food with magnets.

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AndrewJ

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29/01/2026 5:27 pm

@swwils On my Cosy9 when it is working hard, the blown air is noticeable at a height difference of 3m, horizontal distance of 1.5m and through triple glazing (i.e. from the unit below my bedroom window to my ear lying in bed! There is also a noticeable whistling noise from the airing cupboard when it is defrosting (I think that's the case, I only notice it at night if I'm awake and I won't be getting out of bed to check it!) Interestingly, the blown air noise is less noticeable through the triple-glazed kitchen window directly behind the unit.

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swwils

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29/01/2026 6:09 pm

@andrewj mine blown air noise is pretty silent until about 4000W. After that it's noticeable if you are e outside. But mines in a location where blown air noise doesn't matter. But the structure -borne definitely does.

The main pain point is that the control logic seems to ramp the unit to 8000W+ in varying waves for some reason...I can't wrap my head around it other than it's purely hunting for dT.

Hopefully they just release a quiet mode that caps the max output and people agree yes it will reach set point slower and cost slightly more to run, but it might be what some people want. Certainly me.

In summer it definitely needs a summer mode where it would take longer to charge on DWH to get better COP, no need to rush if there is no heating load

My gut feeling is that they have a lot of flow rate headroom and can make some really nice software tweaks.

Also if you have a look at my MID monitoring, my cosy 9 is not running "at is best" and the performance is still actually really great... Compared to the boiler it replaced.

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