Daikin Altherma EKHBH Series Service Manual page 131

ESIE06-03
"U4" Signal Transmission Error (between Hydro-box and Outdoor Units)
4.4
U4
Error code
Method of The data received from the outdoor unit in hydro-box-outdoor unit signal transmission is checked
malfunction whether it is normal.
detection
Malfunction When the data sent from the outdoor unit cannot be received normally, or when the content of the data
decision conditions is abnormal.
Supposed causes
Part 3 – Troubleshooting
Faulty outdoor unit PCB.
Faulty hydro-box PCB.
Hydro-box-outdoor unit signal transmission error due to wiring error.
Hydro-box-outdoor unit signal transmission error due to disturbed power supply waveform.
-outdoor unit signal transmission error due to breaking of wire in the connection
Hydro-box
wires between the
Hydro-box
and outdoor units.
Error Codes: System Malfunctions
1
3 3
4
5
3–45