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Failing heat pump system - seeking thoughts on a rebuild

 
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Air Source Heat Pumps (ASHPs)
Last Post by JamesPa 4 minutes ago
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 JamesPa
(@jamespa)
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Joined: 2 years ago
Posts: 2816
06/09/2025 8:06 pm  

Posted by: @cleardene-ashp
↑

So expecting it to also hit 50 - 55 for DHW seems a stretch to me.

You cant infer the temperature it will do when heating DHW from the temp it does when space heating because the load is different.  When its heating the DHW it is only heating the DHW so should reach the max temperature that the ASHP is capable of, most likely 55. 

As a concrete example my 7kW ASHP reaches 75 when heating the DHW, but runs at <40 most of the time.  On the coldest days it just gets to 45 when doing space heating, but it will still do 75 when its doing the DHW.  Mine has R290 refrigerant so is inherently capable of higher flow temperatures.  Yours is R410 so will be capable of 55.

Posted by: @cleardene-ashp
↑

All of this discussion I’ve insisted here is possibly a bit premature because I first need to reach the point of the company formally agreeing what problem I have.

Agreed.  

 


This post was modified 2 hours ago by JamesPa
This post was modified 1 hour ago 2 times by JamesPa

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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 Cleardene-ashp
(@cleardene-ashp)
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Topic starter 06/09/2025 8:13 pm  

Posted by: @jamespa
↑

When its heating the DHW it is only heating the DHW so should reach the max temperature that the ADHP is capable of, most likely 55. 

Ahh!

ok thanks for that. It’s a small but very significant detail that had escaped me.



   
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 JamesPa
(@jamespa)
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Joined: 2 years ago
Posts: 2816
06/09/2025 8:22 pm  

Posted by: @cleardene-ashp
↑

Posted by: @jamespa
↑

When its heating the DHW it is only heating the DHW so should reach the max temperature that the ADHP is capable of, most likely 55. 

Ahh!

ok thanks for that. It’s a small but very significant detail that had escaped me.

Indeed.  Once you know whether its fixable or not please post back with more detail about the system if its not.  Dont be suckered into replacing more hardware than you need to for the convenience of the installer, from what you have said about how you operate it its quite likely that there is 10% spare capacity which will be sufficient for your DHW unless you have a very high demand.  The collective intelligence here will help minimise the probability that you pay more than you need to.

 


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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 Cleardene-ashp
(@cleardene-ashp)
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Posts: 7
Topic starter 06/09/2025 8:36 pm  

Posted by: @jamespa
↑

please post back with more detail

Will do! Thanks for everyone’s thoughts so far, it’s already helped understand things better.



   
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 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 2 years ago
Posts: 2816
06/09/2025 9:35 pm  

@cleardene-ashp  

Thinking about this the worst case scenario, should the existing system not be repairable, is very probably: plumb the DHW to the heating ASHP; use the immersion to supplement on the few days each year when ASHP has insufficient capacity.    The great thing about this solution is you can 'suck it and see' without doing any calculations.  If the ASHP does have sufficient spare capacity you just never use the immersion! 

Obviously we cant be absolutely certain that's feasible without more detail, but very likely it is.


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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