Vitocal 200-s mixes DHW

[aconjaer]

Hi community,

I have a Vitocal 200-s heat pump which supplies both the DHW and heating. I notice that my DHW temperature in the boiler decreases way too fast (from 45°C to 38°C in 5 hours). However, when I completely shut down the heat pump, the temperatures remains stable for a much longer period. In the attached picture below, I've shut down the system between 22pm and 6 am. In this period the temperature only decreased 3°C over 8 hours. This made me think that mixing occurs between DHW and the heating circuit. A Viessmann technician already replaced the 3-way valve, so I think it's unlikely this is the cause. Is there anything else I'm missing out here?

Kind regards,

Andreas

[BernhardW1]

Do you have a circulation pump installed (and running)?

[aconjaer]

I do have a circulation pump, but even when I shut it off and close the valves on the circulation circuit, the temperature still decreases.