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

I don't know how it is with the SOL, but in principle you can adjust the cycles of the HKP on the LWZ. You can try setting 19 degrees at "AT Zyklen max" (or something similar) and the "Zyklen max." to the maximum value, for testing. Oh, and make sure you are not in summer mode, meaning heating mode off because of AT. That can also be set.

The system has been in place since 2013, but we only bought the house this month. Summer operation is currently set from 20°C AT, which should still be fine.

Cycles Min and Max are 0 / 100 and temperatures are at 25/0. In other words, at an AT of 25 (due to solar use) it no longer runs a heating pump cycle and at 0 and below 50.

Would the following be possible? Due to the low AT at night (e.g. 0 degrees -> 100 cycles) and in the early morning hours, a few pump cycles are already needed there (e.g. 45). If the AT then increases and the sun shines, at 18 degrees for example only 40 cycles would be allowed (if this moves dynamically) and thus the pump would no longer run.

Wrong approach, or possible? If possible, I should probably increase the AT MIN cycles further...

Summer operation is set from 20°C AT

What hysteresis? In summer operation, the pump runs normally at the minimum value.

Cycles Min and Max are 0 / 100 and temperatures at 25/0.

I wouldn’t do 0. Circulating the heating water once definitely won’t hurt.

If the AT now rises and the sun shines, for example at 18 degrees only 40 cycles would be allowed (if this moves dynamically accordingly) and thus the pump would no longer run.

I don’t think it works like that, i.e. with an accumulation over 24h and a "remaining quota." Normally the pump always interpolates to the current AT.

Just set it higher to try it out. Trying is better than studying.
288 cycles should be the maximum and thus continuous operation.

1/100 was set, I had made a mistake while writing. Sorry. I am now running FHEM and am a bit less flying blind with the system (including when it is winter/summer). However, many short compressor starts are bothering me now, which I cannot explain:

Yesterday (I had deactivated the ventilation for a short time in the evening here, hence the "pause" in the 4th chart):


Today:


You can see that the heating pump (3rd chart, black line) runs continuously from a certain point on and no longer just "feels" briefly, and then the integral value is repeatedly reset – but the compressor only runs for a very short time (0.5–1 sec) and then immediately switches off again. This resets the integral value, but since the temperatures have not changed, the integral value naturally drops right away. What possibly faulty setting could this be due to? Is this normal? Flow is present as mentioned, and the compressor usually runs and heats well.

Here is a current chart with more data:

Phew, you’re throwing out riddles here. But cool curves ;)
No idea if the behavior has anything to do with solar, I have no clue about that.

What do you mean the compressor runs for 1 sec.? You mean every time the integral was reset it twitched? Seen live?
Because I’ve never seen the reset like that either.

The only thing I notice now:
During the cycles in the morning the return flow increases very quickly. Hard to tell from the scaling, but somehow that looks too fast.
Can you rule out a hydraulic short circuit? How about ERR and ÜSV?
Does the Vd always run normally long with the solar pump? Or is that just a coincidence now?

Do you actually operate 100% return flow controlled?
What I and P values have you set?

Maybe you could also check in the FingerHau s For, they have mostly LWZs and FHEM.
Or also sometimes in the HTD.