To revisit the topic: What do you recommend regarding the activation or switching on of the FW for hot water generation? I was thinking: Starting in May (good sunshine, summer is coming...), I would only switch on the FW for hot water generation from late afternoon, maybe 3 p.m. to 9 p.m. This ensures that a) there is still enough hot water in the morning for the morning routine. b) No further heating of the water occurs in the morning, so that the water is as "cool" as possible to absorb the heat amount from the ST system.
According to my understanding: If I have already reached the target temperature in the boiler at noon, then the FW for hot water preparation should not switch on. There must be a control system that checks the actual temperature of the hot water in the boiler and then, if necessary, heats the water to the target temperature. If this is already reached, no heating is necessary, right? It is probably only about the case when, in the evening, the boiler is empty or the mixing temperature drops again due to the inflow of fresh, cold water, and because of the time of day (evening) no heating takes place through the ST system anymore, then it is ensured that the water is heated with the FW.