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Domestic Hot Water & Cylinders
Last Post by Toodles 9 months ago
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 Somerpark
(@somerpark)
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Joined: 9 months ago
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Topic starter 27/02/2025 5:14 pm  

Hi 

I am in the process of getting a heat pump. At present I have a Mira Platinum low pressure pumped digital shower, and assumed all I had to do was replace it with the high pressure version. When looking at this option I read the spec for the unit which stated the hot water operating temp. range was 55-65 degrees. As I want to store water in the range 48-50 degrees I emailed Mira customer services to ask if it would work ok.

The reply was vague, offhand and unhelpful "Don't know we haven't tested it at that temp, may work my not or not work as well as it could/should, any issues will invalidate your warranty" so not a lot of help there.

Any heat pump owner using something similar, does it work ok, I assumed anyone using a combi gas boiler would not be heating water to around 60 degrees so it should work?  



   
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Morgan
 Morgan
(@morgan)
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27/02/2025 6:12 pm  

I had a Aqualisa digital pumped shower prior to having the ASHP installed’. It had to be stripped out because the ASHP system is a closed mains pressure system and consequently cannot have a pumped/power shower.  Swapped it for a non pumped shower. 

 


This post was modified 9 months ago by Mars

Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.
14 x 500w Monocrystalline solar panels.

2 ESS Smile G3 10.1 batteries.
ESS Smile G3 5kw inverter.


   
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 Somerpark
(@somerpark)
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Topic starter 27/02/2025 6:28 pm  

Did you swap it for a another digital unit and is it working ok?

 



   
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 IanMK13
(@ianmk13)
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27/02/2025 6:39 pm  

Surely you could keep a vented DHW cylinder and existing cold water tanks.  Also, why can't the ASHP primaries have a header tank like my gas central heating system?



   
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 Somerpark
(@somerpark)
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Joined: 9 months ago
Posts: 7
Topic starter 27/02/2025 6:54 pm  

That may be possible, I don,t know but why would you want the worst of both worlds?  poor hot water pressure to taps & showers especially upstairs with a big imbalance between mains pressure cold and gravity fed hot and a pair of tanks sitting in the attic, when you can have high pressure hot & cold supply and a large tank of stored water?



   
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 Somerpark
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Topic starter 27/02/2025 7:31 pm  

@morgan

Hi Did you swap it for a another digital unit and is it working ok?

 



   
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 IanMK13
(@ianmk13)
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Joined: 3 years ago
Posts: 194
27/02/2025 10:26 pm  

@somerpark Mains water pressure isn’t necessarily high pressure. Minimum service level is around 1 bar. It may not be the case that there is a large pressure imbalance between hot and cold supplies.  A pumped thermostatic shower overcomes these issues and it is likely that it would be incompatible with an unvented cylinder. 



   
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 Somerpark
(@somerpark)
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Joined: 9 months ago
Posts: 7
Topic starter 27/02/2025 11:41 pm  

@ianmk13 I though mains pressure of 1 bar and above was considered high pressure. and I have been using a pumped digital shower because I have a vented DHW cylinder at present with the associated cold tank and CH header tank in the attic. The pump only overcomes the issue with the shower, my upstairs bathroom hot tap has a 2 metre head, 0.2 bar and my cold tap is mains pressure in my case about 1.5 bar. The heat pump as far as I know only works with an unvented cylinder at mains pressure so it is not an option to stick with my current setup which I would not choose for my situation if it was possible. So the pumped shower has to go.



   
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Morgan
 Morgan
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28/02/2025 7:52 am  

Posted by: @somerpark
↑

@morgan

Hi Did you swap it for a another digital unit and is it working ok?

 

@somerpark

No. I swapped it for a non-digital, unpumped shower, and the cold water storage tank was removed. A power shower is not compatible with an unvented closed system. (As explained by my installer.)

 


Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.
14 x 500w Monocrystalline solar panels.

2 ESS Smile G3 10.1 batteries.
ESS Smile G3 5kw inverter.


   
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Morgan
 Morgan
(@morgan)
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Joined: 5 years ago
Posts: 677
28/02/2025 7:59 am  

Posted by: @ianmk13
↑

Surely you could keep a vented DHW cylinder and existing cold water tanks.  Also, why can't the ASHP primaries have a header tank like my gas central heating system?

@ianmk13 

How will you heat the water in the retained vented DHW cylinder?  Because you won't be using the ASHP.

 


Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.
14 x 500w Monocrystalline solar panels.

2 ESS Smile G3 10.1 batteries.
ESS Smile G3 5kw inverter.


   
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 IanMK13
(@ianmk13)
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Joined: 3 years ago
Posts: 194
28/02/2025 8:05 am  

@morgan  Why not?  There’s hydraulic separation between the ASHP flow and the domestic hot water.



   
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 Somerpark
(@somerpark)
Active Member Member
Joined: 9 months ago
Posts: 7
Topic starter 28/02/2025 8:25 am  

@morgan It won't be retained, new unvented cylinder with the new ashp all old tanks removed with old gas boiler


This post was modified 9 months ago 2 times by Somerpark

   
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