Heat pump LWZ 403 Sol high supply + return in solar thermal. Underfloor heating is malfunctioning...

Hello dear forum,

when the LWZ 403 Sol solar thermal system is active with us, the underfloor heating somehow does not work properly - at least the heating circuit pump does not seem to run. (AT 18.6°C)

Flow temperature: 58.7°C (normally of course significantly lower, but with high heating of the hot water, this is probably fine)
Return temperature: 54.6°C
Setpoint HK1: 25.2°C
Actual value HK1: 59°C
Setpoint HK2: 25.3°C
Actual value HK2: 59.2°C

The heating circuit pump does not run at all during the day as long as the sun is shining and the temperatures are correspondingly high to charge the hot water (max. 65°C).

Since the "actual value" of the heating circuits is so high, the pump probably does not start either?! What could be the problem here?

Hi,
how does the hydraulics look? There is definitely a mixer, right?

An external mixer is not known to me at the moment - at least outside the heat pump I do not see one. The supply from the solar goes directly to the supply input on the heat pump. Internally, there is apparently one for the two heating circuits, if I interpret the manual correctly.

Hi,
please check the documents again for the hydraulics and how the solar thermal system is exactly integrated and controlled.

The basic structure is understood, and hopefully the settings are also correct. Even taking the sensor locations into account, the behavior is not clear to me.

This is how it looks in the LWZ 430 Sol:

Hm, you would need to know how the solarwärme transmitter works. What does the heating engineer say? When was the system put into operation? Maybe 18.6°C outdoor temperature is also too high and the heat pump switches off the heating circuit pump? How was it at cold temperatures?