Ice formation brine pipe heat pump

Heating circuit distributors are all open, you can also feel a slightly warm floor in the bathroom, for example. A 170l buffer tank is integrated in the Viessmann. There is nothing more...

The 170l is your domestic hot water; the buffer tank is a white box that hangs in the heating return line.

The message "flow temperature too low" confuses me. Possibly there is still air in the underfloor heating.

I think the message refers to the flow of the brine circuit. That also makes sense with the negative temperatures.

Oh, we don't have an additional white box, so probably no buffer tank. Yes, the primary circuit is the brine, right? It says the flow temperature is too low.

The short cycles indicate that the heat pump cannot remove the heat and the circuits are closed. However, this does not explain why the heat pump is pushing so hard into the heating circuit in this weather. The Viessmann heat pump is controlled by outdoor temperature and return temperature. What does the outdoor temperature sensor say?

The short cycles indicate that the heat pump cannot get rid of the heat and the circuits are closed. Still, this does not explain why the heat pump is pushing so hard into the heating circuit in this weather. The Viessmann heat pump is controlled by outside temperature and return temperature. What does the outside temperature sensor say?

and what is the return temperature and setpoint from the heating circuit?

You can already tell that the floor is slightly warm, in the bathroom you notice it the most because a higher temperature has been set here.

The outdoor temperature sensor currently reads 18° but is corrected by -1.5°. The flow and return temperature of the heating are currently 24°. However, the system has not been running for a while since I turned off the cooling circuit....

The heat pump has a fixed differential of 5°C + 2 adjustable values for the hysteresis of the return temperature (standard at -2°C for compressor ON and +2°C for compressor OFF).

Example heating curve at 30°C supply target value at 10° outside temperature:
Compressor ON at 23°C return
Compressor OFF at 27°C return