Dimplex SI8TU ground source heat pump - strange behavior

The heat exchanger in the hot water storage tank could be too small or dirty. If I remember correctly, there should also be a filter somewhere before the [WT]. Then the heat pump will not be able to dissipate the heat properly and the spread decreases. This would also fit the [HD] fault in hot water.

If the WT is too small, this would be a design flaw. But it is not the only model used by customers. @TE: Then there is probably a system error or defect, because higher temperatures are required in hot water operation than in heating operation. What output does the heat pump provide when preparing hot water? Have you ever paid attention to that? Constantly 8 kW?

The system is 8 months old and we have very soft water. I dug out the planning scheme from the documents; maybe someone can make use of it. I don't understand a thing about it.

I cannot display the output power of the heat pump, only the power consumption of the compressor. It is constantly around 2300W during hot water production, slightly less during heating operation, in the range of 1900-2100W.

To not leave this as an open question here and in case someone has a similar problem later:

A technician was here and looked at the system. A control valve is defective, so the system cannot regulate itself. This causes the internal pressure to be twice as high as normal despite reduced performance, which then triggers the high-pressure fault. The error has nothing to do with cooling and hot water; the defect was probably there from the beginning but has only now become noticeable through faults due to higher brine temperatures.

The temperature differences between supply and return in hot water preparation have also been clarified: The heat pump only has one temperature sensor for the return flow, and it is located in the heating circuit, so it is not integrated into the circuit during hot water preparation and therefore shows nothing useful.

The control valve will be replaced soon, then we will see further. However, it will be a major operation, installation time about 4 hours.