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Hitachi Heat Pump being replaced with Vaillant

 
Air Source Heat Pumps (ASHPs)
Last Post by trebor12345 1 month ago
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trebor12345
 trebor12345
(@trebor12345)
Estimable Member Member
Joined: 2 years ago
Posts: 179
Topic starter 26/05/2026 3:03 pm   [#3022]

Today we start the replacement of our 2-year-old split 7kW Hitachi Heat Pump.  Being replaced with a Vaillant aroTHERM plus 3.5kW.  The unit is being replaced because it’s over sized for the property and has so many quirks:

  • Requires constant management, which a non-technical person could not to manage
  • Performs defrost even at OAT 15C
  • Poor COP during defrosts and cold periods
  • Defrosts every 35mins irrespective of evaporator or outside temperature
  • Erratic performance, have to turn off to reset
  • Split system not suitable for this property
  • HP is operating close to its minimum operating performance characteristics
  • Short cycling is managed by a SW fix which monitors temperature Flow Temp and waits for a 2C drop before restoring heat.

As Mars would say “Its like managing a patient on life support”.

Today’s activities:

  • Returned R32 refrigerant to HP
  • Removed Heat Pump and Internal Water Storage unit (125Kg)
  • Hole drilled in slab for defrost drainage
  • Vaillant HP and Water Storage placed
1
6
2
5

2024 build bungalow, Southern England, 179 m2, 14w/m2
Underfloor heating, fully open
Vaillant aroTHERM plus 3.5kW
50 litre volumiser
3.6KW solar panels


   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 5123
26/05/2026 3:14 pm  

Great news that work has started but...is that a 4 port buffer I see before me, its auxiliary pump to the right?  If so I strongly recommend to get it replumbed as a volumiser.  Your UFH is all the buffer needed and more besides!


This post was modified 1 month ago 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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trebor12345
 trebor12345
(@trebor12345)
Estimable Member Member
Joined: 2 years ago
Posts: 179
Topic starter 26/05/2026 3:17 pm  

Posted by: @jamespa
↑

Great news that work has started but...is that a 4 port buffer I see before me, its auxiliary pump to the right?  If so I strongly recommend to get it replumbed as a volumiser.  Your UFH is all the buffer needed and more besides!

Yes to be configured as a volumiser.  The pump is to be removed.

 


2024 build bungalow, Southern England, 179 m2, 14w/m2
Underfloor heating, fully open
Vaillant aroTHERM plus 3.5kW
50 litre volumiser
3.6KW solar panels


   
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1
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trebor12345
 trebor12345
(@trebor12345)
Estimable Member Member
Joined: 2 years ago
Posts: 179
Topic starter 27/05/2026 9:11 pm  

Today.  Just the copper pipe work around the cylinder.

IMG 4077

2024 build bungalow, Southern England, 179 m2, 14w/m2
Underfloor heating, fully open
Vaillant aroTHERM plus 3.5kW
50 litre volumiser
3.6KW solar panels


   
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1
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 5123
28/05/2026 8:38 am  

@trebor12345 Nice use of spare ports on the buffer turned volumiser to connect various bits!


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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trebor12345
 trebor12345
(@trebor12345)
Estimable Member Member
Joined: 2 years ago
Posts: 179
Topic starter 29/05/2026 6:17 pm  

Job completed today.  I believe I am happy with the quality of the install.

IMG 4082
IMG 4084
IMG 4083

 


2024 build bungalow, Southern England, 179 m2, 14w/m2
Underfloor heating, fully open
Vaillant aroTHERM plus 3.5kW
50 litre volumiser
3.6KW solar panels


   
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1
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trebor12345
 trebor12345
(@trebor12345)
Estimable Member Member
Joined: 2 years ago
Posts: 179
Topic starter 29/05/2026 7:00 pm  

Post deleted, my error.


This post was modified 1 month ago 7 times by trebor12345

2024 build bungalow, Southern England, 179 m2, 14w/m2
Underfloor heating, fully open
Vaillant aroTHERM plus 3.5kW
50 litre volumiser
3.6KW solar panels


   
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Batpred
 Batpred
(@batpred)
Noble Member Member
Joined: 2 years ago
Posts: 1066
29/05/2026 7:00 pm  

Also not bad in terms of duration, showing that in case of a failure of a heatpump, a new one can be swapped into position in a few days..


8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC


   
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trebor12345
 trebor12345
(@trebor12345)
Estimable Member Member
Joined: 2 years ago
Posts: 179
Topic starter 29/05/2026 7:07 pm  

Posted by: @batpred
↑

Also not bad in terms of duration, showing that in case of a failure of a heatpump, a new one can be swapped into position in a few days..

4 days, but it was an easy install for them.

 


2024 build bungalow, Southern England, 179 m2, 14w/m2
Underfloor heating, fully open
Vaillant aroTHERM plus 3.5kW
50 litre volumiser
3.6KW solar panels


   
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