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Has anyone seen this problem before? Huge anticycling times

 
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Air Source Heat Pumps (ASHPs)
Last Post by JamesPa 4 weeks ago
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 jamesh
(@jamesh)
New Member Member
Joined: 10 months ago
Posts: 6
20/11/2025 3:07 pm  

For the information of others. Vaillent came today, checked everything and decided to change the electronic circuit board in the machine. Hopefully this is a final fix and it's not all good - as winter is just about to hit properly. 



   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 5358
07/08/2026 5:00 pm  

Posted by: @cg360
↑

The faults are:

F703 - low pressure

F585 - sensor fault capac. outlet temp

F520 - sensor fault building circuit flow temp

F519 - sensor fault building circuit return temp

F73 - building circuit water pressure

The fault goes away if I turn off the house mains and switch it back on. But how long it will work for is another question. I've reset the mains seven times today just to heat the hot water.

Im now getting the exact same fault list after 2 years of trouble free operation.  I am faintly suspecting overheating (the heat pump is on a south facing wall and the top gets too hot to touch; the main circuit board is just underneath!) and/or marginal circuit board.  I have heard that its a 'known problem'.  Is there any more intelligence anyone can share before I call Vaillant (I have also put a sunshade over it to test the 'overheating' theory)

 


This post was modified 4 weeks ago 4 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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 cg360
(@cg360)
New Member Member
Joined: 3 years ago
Posts: 4
Topic starter 08/08/2026 12:23 am  

Mine was replaced as they couldn’t fix and couldn’t identify the fault. But mine is on a north facing wall and gets very little sun, fault occurred all year so i doubt overheating was the issue in my case. Good luck!



   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 5358
08/08/2026 8:30 am  

Posted by: @cg360
↑

Mine was replaced as they couldn’t fix and couldn’t identify the fault. But mine is on a north facing wall and gets very little sun, fault occurred all year so i doubt overheating was the issue in my case. Good luck!

Oh dear.  Glad it was replaced.  I have been mighty impressed up until now this is shaking me a bit.

 


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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