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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JamesPa

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10/12/2025 1:16 pm

Posted by: @andrewj

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He checked the settings, again, and said that the WC max temp setting of -3.2c was too warm and should be something like -10c - in other words, the max flow temp of 50c was being applied at -3.2c rather than, say, -10c. By changing this value, actually to -7c after consultation with the Design Team, it effectively means that my Max Flow temp has been lowered below 50c at the sorts of temps I've had problems with.

Great, this is something of a breakthrough. You could presumably reduce it all the way to -10 (or lower?) if necessary

Posted by: @andrewj

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All the radiators were rebalanced and I've been told to adjust internal house temps either by adjusting the Set Point temperature (i.e. the temp the thermostat attempts to reach) and/or the TRVs. It would seem that Octopus are pretty adamant that their heat pumps should be thermostatically controlled.

Make no mistake and don't be fooled, thats for their convenience not your comfort or operating efficiency!

Posted by: @andrewj

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They are also going to arrange a re-survey of the house which will be interesting. I'm really hoping that doesn't lead to a suggestion to downsize radiators.

If they do (and assuming you are happy with the physical size of the radiators) I suggest you tell them politely but firmly where they can put the downsized radiators (hint, not in your house!).

This post was modified 4 hours ago 4 times by JamesPa

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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AndrewJ

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Topic starter 10/12/2025 1:46 pm

@jamespa yes, I'm under no illusions but in some respects, I've made my bed by going with Octopus. I've sort of proved it will work without the thermostatic control, with the last element being the Flow Temp setting which I couldn't adjust further. I think I could probably dive in and adjust that set point from -7c to -10c if needed but initially at least I need them to see it working or not. I do have a direct line to the Design engineer who said I should call if there are problems and he can walk me though making changes in the Cosy Hub.

The re-survey will be undertaken with version 2 software (whatever that means) so all I can do is wait to see what that comes back with. I really don't want to get into an argument about changing radiators and would certainly prefer a flow temperature based fix but concomitantly, I don't want to be getting into arguments about support either so it may be tricky. I would have thought that it would be cheaper for them to try and resolve with flow temp changes first before changing radiators, and in fairness to them nobody has actually specifically mentioned changing radiators! Part of me is actually hoping they say you could get away with a Cosy 6 because it's a much smaller unit.

I'm not unhappy with Octopus (except maybe the promise-to-call-back-and-never-doing-so which infuriates me and has prolonged this experience) and I genuinely feel they want to get it sorted for me. Anyway I will add to the tale as things progress. What a journey!!

👍

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