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Mitsu Zubadan flow temperature issue

 
Air Source Heat Pumps (ASHPs)
Last Post by bontwoody 2 days ago
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bontwoody
 bontwoody
(@bontwoody)
Noble Member Contributor
Joined: 4 years ago
Posts: 963
Topic starter 05/01/2026 3:43 pm  

Ive been doing some work with a 12kW Zubadan system that wasnt performing well. Ive established that it is oversized and sorted out some poor insulation problems. It appeared to be running nicely (if rather hot) as shown by the plots below:

{264A9B26 DB21 4C93 8649 53153DF8623B}

The owners have always struggled to heat the house adequately in cold conditions so I was interested to see what happened in this cold snap. The next day at about 8.30pm I had a message to say that they were cold, as I cant adjust the WC curve remotely, I switched to a fixed flow temperature of 55C. The red line shows the target flow temperature.

{91333117 75ED 44B1 8255 41D4E0738827}

Unfortunately the flow temperature started to oscillate wildly, with the mean temperature probably reducing. The next day shows the problem clearly with the target flow temperature not being even nearly achieved.

{A3E531EE DA72 48F4 A993 2F6932A80787}

Today, I managed to get to site and upped the WC curve at about 12 noon.

{8E1D0113 7668 439B 82A6 0A24FE03E7DA}

However the average flow temperature stayed well under target, so about about 3pm I switched to a constant flow temperature of 60C, but this still doesnt seem to be raising the average flow temperature.

Does anyone have an idea what is going on? The heat pump does have some fin damage due to being powerwashed. The radiator temperature was at about 38C when I was there, well below the flow temperature, this is after the pipework in the loft was reportedly insulated. Thanks in advance


House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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bontwoody
 bontwoody
(@bontwoody)
Noble Member Contributor
Joined: 4 years ago
Posts: 963
Topic starter 05/01/2026 4:55 pm  

Update: The flow temperature has now stabilized at 60C as required, unlike the 55C constant flow temperature yesterday. Im going to leave it a while and if it stays that way switch back to the WC curve.

{D08801E6 7C4B 4CBA AD60 5636A81CECBD}

House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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