District heating transfer station, high energy consumption

Hello everyone,

At the beginning of this year, I bought a used house (built in 1978). An oil heating system was installed in 2006, and in 2020, district heating was added. The latter is supplied to us by the neighboring farmer through a biogas plant. From April to November, we had a consumption of 35,000 kWh!!! Without even running a single heater. In my opinion, the high energy consumption is due to the temperature fluctuations of the district heating (60 - 90°C). Our buffer tank is heated up to 90°C and then the temperature drops back to 60°C. Then 90°C again, and so on... As can be seen in the pictures, we do not have a transfer station but a direct flow through the heating coil of our buffer tank. The previous owner apparently tried to install a control system using the devices shown (actually intended for solar use). I have currently turned off the district heating and operate the heating + hot water with a fraction of the energy.

Question: Which device is suitable as a control unit to continuously heat the buffer tank to around 65°C and avoid wasting unnecessary energy?

Thank you very much for your help,

Markus

Wild construction. Malleable cast iron, red brass, stainless steel, and copper over a very short distance, someone was cleaning out their stock. Also fits with the "MSR".