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Hot water tank lose heat rapidly on random days

 
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Air Source Heat Pumps (ASHPs)
Last Post by Bash 2 months ago
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 5021
21/04/2026 8:14 pm  

UFH = underfloor heating.

Can you check any part numbers on this valve, something odd here unless it's a being used as a temperature operated switch to avoid a power lead.  Has anything else changed since it all worked ok?


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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 Bash
(@bash)
Reputable Member Member
Joined: 8 months ago
Posts: 211
21/04/2026 11:24 pm  

@bazcurtis 

We had one of these Esbe valves fitted as part of our recent install.

We had a similar issue. The hot water tank temperature would drop rapidly after a reheat and the radiator temperatures were much hot than expected.

The installers immediately knew there was an issue with the Esbe valve not function correctly.

They suggested the valves can be easily installed/setup incorrectly.

The replaced the valve and it is now diverting correctly.

You can visibly see it moving (and hear it) when the dhw recharge starts/ends.

No more heat loss into the rads once it was corrected!



   
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 bazcurtis
(@bazcurtis)
Active Member Member
Joined: 1 year ago
Posts: 20
Topic starter 22/04/2026 9:11 am  

@jamespa @bash Thank you very much for the information. I am going to chase up the installer today. Just to round this off for @jamespa, we don't have UFH and these are numbers I could find

ARA655

12120911

 

 

IMG 1082


   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 5021
22/04/2026 9:29 am  

@bazcurtis 

Contacting the installer is the thing to do

 

I note from the online description of this part:

 

  • Reliable and quiet operation
  • Can be used for both 2-point and 3-point control signal
  • Perfect match between the actuator and ESBE valve

The bullet in bold rather suggests the possibility to set it up incorrectly!


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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 bazcurtis
(@bazcurtis)
Active Member Member
Joined: 1 year ago
Posts: 20
Topic starter 22/04/2026 9:41 am  

@jamespa I have called them this morning. I will update this thread when they try a fix and what it was. Thanks for all the help.



   
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 Bash
(@bash)
Reputable Member Member
Joined: 8 months ago
Posts: 211
22/04/2026 1:19 pm  

@jamespa 

Our installer said the same. You need to adjust it inside and can be easy to overtighten or get it set incorrectly. In the end they just replaced ours as it was a brand new install.



   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 5021
22/04/2026 1:30 pm  

Posted by: @bash
↑

@jamespa 

Our installer said the same. You need to adjust it inside and can be easy to overtighten or get it set incorrectly. In the end they just replaced ours as it was a brand new install.

Goodness knows why they fit this rather than a conventional diverter-only valve.  Its a nice (and jolly expensive) valve for sure, but the more you leave up to the installer the more there is to go wrong!  Doubtless they have their reasons.

 


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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 Bash
(@bash)
Reputable Member Member
Joined: 8 months ago
Posts: 211
22/04/2026 1:55 pm  

@jamespa 

Hopefully their reasons are well intended! They did say that it is better than what they used to install. Time will tell whether that proves to be correct!



   
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