Is optimization of the heating system possible after hydraulic balancing?

The shift would only be for the transitional period; when it gets colder again, you reset it.

The 20 degrees of the heat pump is a fictitious value since it does not know the temperature in the rooms.

This value is used internally by the heat pump to adjust the supply temperature or the return temperature
in relation to the outside temperature.

Were the L/M values read on the distributor or taken from the documents?

"I don’t know how this is supposed to be achieved, since we have set a single temperature on the heat pump (it is currently set at 20°C)."

The different temperatures for rooms are achieved at a constant supply temperature by the amount of water flowing through.
Rooms that need to be warmer require more water, others less.
The temperature on the heat pump is not the expected room temperature (see above).

https://www.hausbau-forum.de/threads/zentraler-raumtemperaturregler-fuer-err-der-fbh.35503/page-7#post-417306

Then please take a picture of the heating circuit distributor. Different temperatures in the rooms are achieved through different flow rates. You can also adjust the flow rates at the heating circuit distributor. Reduce the flow at the HCD for the bedroom, then you can leave the room sensor set to max. Maybe you can also give a little more flow in the bathroom via the HCD. But then you are already in the middle of the hydraulic balancing. The ideal time for this is actually over, but a little regulation in the bedroom is still possible.

I also found a planning note from the executing company for the underfloor heating in the documentation I recently received, stating "underperformance" for the bathroom of 49W, indicating additional heating surfaces were necessary. :/ However, we do not have these. During the selection process, we discarded the towel radiator, with the justification that it wouldn't really get warm at often below 30°C flow temperature. What we did not consider or know at the time was that it probably would have helped us to heat the bathroom overall a bit more.

That’s true. I have also often read that bathrooms cause problems because there is no underfloor heating under the tub and shower, so the heating surface area for the room volume is very small. In some cases (as with me) there are also air extraction devices that naturally draw the cooler air from adjacent rooms into the bathroom. But the 1.8 m high towel radiator without an active heating cartridge hardly does anything for us, even at a comparatively somewhat higher flow temperature. The most pleasant effect only arises from the heating cartridge (600 W) recommended to us and which we commissioned. Of course, that then costs almost €0.20 per hour (with a noticeable effect after 10-15 minutes), while the necessary flow temperature for a similarly pleasantly tempered bathroom would also cost something.

If you feel too warm during the transition period, as mentioned above, you need to set the heating curve steeper. The curve shows the lowest flow temperature at the highest outdoor temperature (OT) in the bottom left (before the heating switches off). And at the top right, the curve shows the highest flow temperature at the lowest outdoor temperature (LOT).

To make it steeper now, there are two options. Depending on the heat pump, you can change all or only some values:

1: You can lower the base temperature. The flow temperature at which the heating starts to heat. Before: 18° OT = 25° flow temperature, after: 18° OT = 23° flow temperature (If applicable, you can also lower the start OT. That means the heating only starts heating at lower temperatures. If the flow temperature remains the same, this also makes the curve steeper.) 2: You can directly adjust the "steepness" of your curve. In new buildings, the value is somewhere around 0.6. You would then set it initially to 0.7. However, since this usually changes the end temperatures, you must then perform a parallel shift downwards afterwards. Probably by lowering the flow temperature at the start and end OT. Sometimes there are also offsets that you can change.

(I am not an expert and have only done this twice myself. If I have mixed up signs or used wrong terms somewhere, please correct me!)

Regarding the bathroom: That is always a tricky thing. The 49 watt undercoverage is not a problem, since a higher room temperature was calculated for it than for the other rooms. After successful balancing, the temperature in the bathroom should also be noticeably above that of the other rooms. If that is not the case, first make sure the bathroom gets the maximum flow. Preferably unscrew the ERR and manually give maximum flow to the bathroom at the distribution box. If the bathroom already has maximum flow, there is only one bitter pill: Then the heating curve must be raised overall. And at the same time, ALL other rooms must be throttled slightly (manually at the distribution box) until the temperatures are right again. But then you operate your heat pump some percentage points less efficiently (because warmer), thus consuming considerably more electricity, just to have a little more cozy feeling for 30 minutes a day. So I wouldn’t do that. Retrofitting a small infrared heater, which is only switched on when the bathroom is used, would be more sensible.

What else comes to mind: Is the bathroom perhaps ventilated more strongly? Through controlled residential ventilation, or frequent tilted windows? Or is the door always open? Both of these naturally lower the temperature even when the heating is properly adjusted...

One more thing: Since you do not use the ERR (which is good), I would switch it off electrically or even remove it entirely.