Error code
U4 Indoor-to-outdoor communication fault
Applies to 15 models
FTXJ20A2V1BW, FTXJ25A2V1BW, FTXJ35A2V1BW, FTXJ42A2V1BW, FTXJ50A2V1BW, FTXJ20A2V1BS, FTXJ25A2V1BS, FTXJ35A2V1BS, FTXJ42A2V1BS, FTXJ50A2V1BS, FTXJ20A2V1BB, FTXJ25A2V1BB, FTXJ35A2V1BB, FTXJ42A2V1BB, FTXJ50A2V1BB
What this means
Communication between the indoor and outdoor units has failed.
When to call a technician
This fault involves refrigerant, pressure, or electrical work that must be handled by a certified technician under EU F-gas rules. Do not attempt to open the refrigerant circuit, access mains wiring, or adjust pressure components yourself. Contact a qualified installer or servicer for this one.