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Octopus Cosy Heat Pump Owners & Discussion Thread

AndrewJ · 2025-10-23T11:37:06Z

I'd like to discuss how you find it, how you run it and so on.

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Air Source Heat Pumps (ASHPs)

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AndrewJ

(@andrewj)

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Topic starter 17/11/2025 4:19 pm

Posted by: @jamespa

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Some tweaks of WC may indeed be necessary, if its too hot both downstairs and up (and its not solar gain) then you definitely need to turn the WC down!

Hot upstairs seems to be a problem with modern houses. With open plan and good insulation, there is literally nowhere for the heat from downstairs to go other than the bedrooms. People on buildhub are now doing newbuilds without upstairs heating other than in the bathroom. This is all a bit iterative, it might take you the whole season to get it spot on. There is also an element of adjusting to constant temperature!

Indeed. I've been out most of the day but monitoring. The downstairs living area was 22.4c at 7am but rose to 23.3 by mid-morning. At 14:30 it dropped by 0.1c and now, at 16:00 it is 23c (and whilst writing this has gone up to 23.1c at 16:18!!) Having turned down the radiators upstairs, temps are reading 23.7c - 24.9c and I've got little room for manoeuvre here as these rads are only open 0.25 turns. So my plan is to leave it overnight to see how it copes as the temp is forecasted to drop to 0c overnight. If I maintain temps then I think I can drop the WC curve; if it doesn't maintain temps (by which I mean the living area sticks around 23c) then I might have to tweak open the downstairs radiators. I have to be careful here though as some of the radiators share a 15mm loop and there would be a risk of starving Peter to feed Paul! I have a feeling that with a couple of upstairs rooms I will need to use the TRVs to limit their temperature but hopefully not.

Anyway, I feel I'm making progress because temps are closer and the daily COP is 4.11

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Toodles

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17/11/2025 4:39 pm

@andrewj Sounds promising; and those LSV’s can be tricky devils, if you have a quarter turn open valves, a tweak might only be a few degrees clockwise to effect a noticeable reduction. (Well worth trying though before resorting to using the TRV’s which are brute force by comparison). Regards, Toodles.

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

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Toodles

(@toodles)

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17/11/2025 4:45 pm

And I might add that the constancy provided by the LSV is much better for the system than the variable effect of a changeable TRV. Using the TRV as an overly-warm limiting device and nothing more is a good starting point when there are other variables like the WC possibly being higher than you may require. Regards, Toodles.

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

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AndrewJ

(@andrewj)

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Topic starter 17/11/2025 4:57 pm

Posted by: @toodles

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@andrewj Sounds promising; and those LSV’s can be tricky devils, if you have a quarter turn open valves, a tweak might only be a few degrees clockwise to effect a noticeable reduction. (Well worth trying though before resorting to using the TRV’s which are brute force by comparison). Regards, Toodles.

That's good to know, thanks. I'll definitely be using TRVs as last resort.

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JamesPa

(@jamespa)

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17/11/2025 6:28 pm

Posted by: @andrewj

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That's good to know, thanks. I'll definitely be using TRVs as last resort.

If LSVs prove troublesome (which they definitely can) take the heads off the TRVs and fit decorators caps. That gives you a much more linear and fine adjustment of flow.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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