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Gen 6 Samsung ASHP losing 20C of DHW in 60 min directly after generation

 
Air Source Heat Pumps (ASHPs)
Last Post by andbeck 2 months ago
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 andbeck
(@andbeck)
New Member Member
Joined: 2 months ago
Posts: 3
Topic starter 04/01/2026 1:18 pm  

Hi all - I have a Gen6 Samsung ASHP linked to a thermal store.  Stratification is (has) supposed to keep the top for DHW.  My temperature sensor for DHW is in the top most slot of the thermal store.

Over the past 2 months, I've had DHW generation set to 50C.  As you can see in the attached graph, I am losing 10C within 30 min and then another 10C over the hour.  It seems to me that my stratification is collapsed, as the temperature is being pulled down very rapidly to my central heating target.  And our radiators get much warmer during the DHW generation.

We have an over-engineered system with a pump each on the flow and return (EMBRASS Peerless) and I've reduced these to speed II, with improved central heating performance (I think) but no change to the DHW issue.

Thanks for any insights.

Screenshot 2026 01 04 at 12.55.47

This topic was modified 2 months ago by Mars

   
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Topic Tags
ASHP Hotwater ASHP heat loss DHW problems
JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 4475
04/01/2026 1:43 pm  

@andbeck

Couple of questions and a thought:  

I cant actually work out in the plot which line is the DHW temperature and which the heat pump flow temperature.  Can you clarify.

 

To respond to your stated position:

Has anything else changed in the DHW system?

I presume it (including surrounding pipes) is well insulated/insulation hasnt changed

Is it possible the diverter valve is slightly stuck, leaking some (cooler) water at space heating temperature through to the coil.  That could account for it.


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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 andbeck
(@andbeck)
New Member Member
Joined: 2 months ago
Posts: 3
Topic starter 04/01/2026 9:53 pm  

@jamespa - thanks for the reply.  

You've made me look at these traces more carefully.  The green trace is what I've been looking at and it's the heat pump heating flow temperature. It can't be the tank temperature as it gets to 50 in 3 min!

The DHW temperature is missing and should be a blue trace labelled as "hot water flow temperature".  I think.  

This suggests that we may have an issue with the sensor...  I'll work on that, and look for any issues with diverters too.

 



   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 4475
05/01/2026 8:38 am  

Posted by: @andbeck
↑

@jamespa - thanks for the reply.  

You've made me look at these traces more carefully.  The green trace is what I've been looking at and it's the heat pump heating flow temperature. It can't be the tank temperature as it gets to 50 in 3 min!

The DHW temperature is missing and should be a blue trace labelled as "hot water flow temperature".  I think.  

This suggests that we may have an issue with the sensor...  I'll work on that, and look for any issues with diverters too.

 

That was what confused me!  The heat pump FT is doing what you would expect.

 


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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 EcoBaker
(@ecobaker)
Trusted Member Member
Joined: 2 years ago
Posts: 45
05/01/2026 10:06 pm  

Shouldn’t your temp sensor be in the middle or lowest sensor pocket? Otherwise you’re not actually heating up much volume of water before the DHW temp sensor get to target and turns off, thus not actually much heat stored. My tank a 200L telford has two pockets one at the top and one around half to two thirds down the tank that is the one I use.


Samsung Gen6 8kw ASHP in a two bed victorian mid terrace.


   
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 andbeck
(@andbeck)
New Member Member
Joined: 2 months ago
Posts: 3
Topic starter 06/01/2026 10:17 pm  

@ecobaker Thanks for this.  I've had it in both slots.  Currently in the top as in the middle it takes much longer and disrupts the heating more - again, I've been managing a temperature loss problem and probably need to replace the sensor.

 

I can't seem to figure out whether the sensor is a bog standard PT 1000 for this situation... do you know?  



   
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Topic Tags:  ASHP Hotwater (2) , ASHP heat loss (3) , DHW problems (2) ,



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