Incorrect DHW tank temp

[luuks123]

I get an incorrect notation in Home Assistant on my DHW tank temperature, what could be the cause of this?

DHW tank temp. (R5T): -40.7

Water pump operation: 'OFF' Indoor Option Code: 11 Outlet Water Heat Exch. Temp. (R1T): 28.5 Outlet Water BUH Temp. (R2T): 27.4 Refrig. Temp. liquid side (R3T): 23.7 Inlet water temp.(R4T): 22.9 DHW tank temp. (R5T): -40.7 RT Temp.: 20.8 Powerful DHW Operation. ON/OFF: 'OFF' Space heating Operation ON/OFF: 'ON' Emergency (indoor) active/not active: 'OFF' LW setpoint (add): 38.5 RT setpoint: 19.5 DHW setpoint: 65 LW setpoint (main): 25 Water flow switch: 'ON'