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

 
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Air Source Heat Pumps (ASHPs)
Last Post by AndrewJ 6 days ago
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 L2jad
(@l2jad)
Trusted Member Member
Joined: 3 weeks ago
Posts: 25
17/02/2026 9:11 am  

As a secondary, how is your water temperature, as you know my sensor was moved to bottom of cylinder yesterday, 2 hours gets to 46 degrees, 3 hours gets to 46 degrees, just boosting to see if i can get to 50? I’m not convinced it will get there. It might shall see!! 
just wondered if people get to 50 on the cosy 12?



   
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 Harriworld
(@harriworld)
Eminent Member Member
Joined: 3 weeks ago
Posts: 13
17/02/2026 9:36 am  

@l2jad Must admit my water is lovely and hot. It is switched on for an hour only and gets to temp quickly. Set at 50.



   
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 L2jad
(@l2jad)
Trusted Member Member
Joined: 3 weeks ago
Posts: 25
17/02/2026 9:49 am  

When sensor was at top it got hot very quickly. Not over bothered as we have a lot of hot water. Just seems to get to a temperature and doesn’t get hotter. 

i’m guessing over the next few days as water in tanks start point is warmer it will sort.

 

pre move of sensor two showers and water was cold 😉



   
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 AndrewJ
(@andrewj)
Reputable Member Member
Joined: 1 year ago
Posts: 189
17/02/2026 11:52 am  

Posted by: @l2jad
↑

As a secondary, how is your water temperature, as you know my sensor was moved to bottom of cylinder yesterday, 2 hours gets to 46 degrees, 3 hours gets to 46 degrees, just boosting to see if i can get to 50? I’m not convinced it will get there. It might shall see!! 
just wondered if people get to 50 on the cosy 12?

The Cosys are/should be capable of heating the tank of water to over 50c, including doing a legionella cycle if you want it.  If it's heating a full tank of cold water it may take more than 2 hours, I don't know, but I assume your schedule for hot water is set with the desired temp to reach.  We have ours set at 45c, usually reaches 46c/47c in one hour; never run a legionella cycle.  There is just the two of us with a 250L tank so we don't get anywhere near emptying it with two showers a day and typical other hot water usage.  I'd say it is never heating from fully cold though, even if my wife chooses to have a bath.

The fact that it is only reaching 46c after two hours and no difference after 3 hours is a bit strange though.  However, I would add this: you can only validly check the temp the app is reporting in the morning BEFORE anyone uses any hot water AND nobody is using hot water whilst you are heating it.  Once that happens, the app is reporting the temperature of the water mixed with cold - e.g. our shower has only been used once today and there's been a bit of hot water usage rinsing cups and brushing teeth: the reported temperature in the app is 26.4c!  It would have been 46/47c first thing and there is still plenty of hot water left at that temperature.

 



   
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