ᐅ Heat pump LWZ 403 Sol: high supply and return temperatures with solar thermal system. Underfloor heating system is not working...

Hello dear forum,

When our LWZ 403 Sol solar thermal system is active, the underfloor heating does not seem to work properly – at least the heating circuit pump does not appear to run.
(Room temperature 18.6°C (65.5°F))

Flow temperature: 58.7°C (137.7°F) (normally, of course, much lower, but this fits since the hot water is being heated intensely)
Return temperature: 54.6°C (130.3°F)
Setpoint HK1: 25.2°C (77.4°F)
Actual value HK1: 59°C (138.2°F)
Setpoint HK2: 25.3°C (77.5°F)
Actual value HK2: 59.2°C (138.6°F)

The heating circuit pump does not run at all during the day as long as the sun is shining and the temperatures are high enough to charge the domestic hot water (max. 65°C (149°F)).

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

Hello,
what does the hydraulic system look like? There is definitely a mixing valve, right?

I am not aware of an external mixer—at least, I don’t see one outside the heat pump.
The supply from the solar system goes directly to the supply inlet on the heat pump.
There is probably an internal mixer for the two heating circuits, if I am interpreting the manual correctly.

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

The basic setup is understood, and hopefully the settings are correct as well. However, even considering the sensor locations, I cannot explain the behavior.

Here is how it looks in the LWZ 430 Sol:

Hmm,
you would need to understand how the solar thermal transfer system works. What does the heating technician say?
When was the system commissioned?
Perhaps an outdoor temperature of 18.6°C (65°F) is too high, causing the heat pump to switch off the heating circuit pump? How did it perform at colder temperatures?