Hi, ok, I see what you mean. You have the following problem, that the high energy, which you transfer from the heat pump to the storage tank, cannot be transferred fast enough to the drinking water via the heat exchanger pipes inside the storage tank. Thus you have the problem that the return temperature is also very fast, very high, here is simply at 60 ° C end - more creates the WP simply not. Since the heat pump cannot transfer any more energy into the pipe, the heat pump shuts down. You must therefore give the water circulating between the buffer and the heat pump more time so that the energy can be transferred to the drinking water. This can be achieved by reducing the speed of the secondary circuit pump during DHW preparation. This reduces the flow velocity and the heating water has more time to transfer its charged energy to the drinking water. At the same flow temperature, the return temperature is colder, thus more energy is transferred to the buffer. But be careful: the speed can only be reduced up to a certain point, otherwise the flow will fall below the minimum flow, and then the heat pump will go on fault. It is therefore advisable to have this adjustment made by the heating engineer or the Viessmann technical service. Regards, Guennie
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