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Finding a Thermostatic Shower Valve That Works with Heat Pump Systems

 
Thermostats, Volumisers, Buffer Tanks, TRVs, Pumps, Piping, Valves, Radiators & Controls
Last Post by Toodles 3 weeks ago
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 ChrisJD
(@chrisjd)
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Joined: 3 weeks ago
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Topic starter 06/11/2025 8:22 pm  

I currently have a concealed thermostatic shower valve, installed 21 years ago, along with a 3-output diverter.

I am currently on the point of ordering a Heat Pump boiler replacement, but am concerned about the lower water temperature this would provide.

I conducted some tests by adjusting my existing boiler. I found that with our current shower (a Bristan PM TSHCVO C with the diverter PM 5WDIV C) which uses a pumped water supply, our chosen temperature is approximately 39°C. This is comfortably achieved with a temperature at the bathroom sink of 66°C.

However, with the sink temperature lowered to 55°C, the shower could only achieve 35°C, which felt too cold. The anticipated 50°C from the heat pump system would certainly not be acceptable.

The original supplier tells me that "All of our showers will require a minimum water feed at 60°C for the showers to perform correctly."

I have emailed several manufacturers and suppliers. Their common response, so far, is very much along the line of "We must inform you that we do not produce thermostatic mixers that are suitable for systems where the hot water supply is only 50°C".

I guess that, in the fullness of time, things may change. Right now, does anybody have knowledge of any thermostatic shower valve which claims to have the necessary lower differential to give, around 40°C output with 50°C input?

The actual experience may differ from my expectations, but it looks as if I may have to take the unwelcome step of running the water tank inefficiently warm.

 

 


This topic was modified 3 weeks ago by Mars

   
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Morgan
 Morgan
(@morgan)
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07/11/2025 7:37 am  

I have a Grohe shower with a 3-way diverter fitted to an Ecodan ASHP. DHW at max 50 °C.  No problems at all.


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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 ChrisJD
(@chrisjd)
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Joined: 3 weeks ago
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Topic starter 07/11/2025 8:43 am  

Posted by: @morgan
↑

I have a Grohe shower with a 3-way diverter fitted to an Ecodan ASHP. DHW at max 50 °C.  No problems at all.

Thanks, that's interesting. Grohe responded to me "we do not produce thermostatic mixers that are suitable for systems where the the hot water supply is only 50 degrees celsius"

Out of curiosity, at the setting you desire, what temperature do you actually get at the shower?

 



   
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Morgan
 Morgan
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07/11/2025 10:30 am  

@chrisjd 

 I don't know, but it's too hot to go full heat and quite hot enough just below the safety stop button.


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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Toodles
 Toodles
(@toodles)
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Joined: 3 years ago
Posts: 2295
07/11/2025 11:37 am  

@morgan Our Mira thermostatic shower system is fed from a Sunamp Thermino ePV210 heat battery via their standard Tempering Valve. This valve is set to maximum and we have no problems at all; we never need to go above 6.5 on the Mira shower setting. I’m sorry, I don’t know what temperature we use but there seems to be plenty in reserve for anyone needing higher temperatures! Regards, Toodles.


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


   
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Toodles
 Toodles
(@toodles)
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07/11/2025 11:45 am  

And as best I can tell from the Sunamp details, the maximum water output temperature is 55 deg. C Toodles.


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


   
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Morgan
 Morgan
(@morgan)
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Joined: 5 years ago
Posts: 673
07/11/2025 2:26 pm  

Posted by: @morgan
↑

@chrisjd 

 I don't know, but it's too hot to go full heat and quite hot enough just below the safety stop button.

@toodles your reply should be addressed to @chrisjd 

 


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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Toodles
 Toodles
(@toodles)
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07/11/2025 2:46 pm  

@morgan I’m sorry, the system doesn’t lend itself to replying after someone else has already done so as the only space given to reply contains the replyee’s reference. I was rushing and had less time than I needed to go back and take things from the ‘quote’ box which is all that was offered. I use extreme magnification to read the text and sometimes unfortunately miss link or text box entry point. Again sorry, will try to do better. Toodles.


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


   
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Morgan
 Morgan
(@morgan)
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Posts: 673
07/11/2025 2:52 pm  

Posted by: @toodles
↑

@morgan I’m sorry, the system doesn’t lend itself to replying after someone else has already done so as the only space given to reply contains the replyee’s reference. I was rushing and had less time than I needed to go back and take things from the ‘quote’ box which is all that was offered. I use extreme magnification to read the text and sometimes unfortunately miss link or text box entry point. Again sorry, will try to do better. Toodles.

@toodles LOL. By my reply, I was only trying to ensure that @chrisjd was notified of your response. You are hereby forgiven LOL.

 


This post was modified 3 weeks ago by Morgan

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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Toodles
 Toodles
(@toodles)
Illustrious Member Contributor
Joined: 3 years ago
Posts: 2295
07/11/2025 3:48 pm  

@morgan I should just have written ‘Mea Culpa’ shouldn’t I? 😉 Toodles.


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


   
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