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Mitsu Zubadan flow temperature issue

Air Source Heat Pumps (ASHPs)

Last Post by bontwoody 9 months ago

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bontwoody

(@bontwoody)

Noble Member Contributor

Joined: 5 years ago

Posts: 1062

Topic starter 05/01/2026 4:43 pm [#2708]

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:

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.

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.

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

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-3 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
10kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60

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bontwoody

(@bontwoody)

Noble Member Contributor

Joined: 5 years ago

Posts: 1062

Topic starter 05/01/2026 5:55 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.