Error code
C4-00 Indoor heat exchanger temperature sensor fault
Applies to 25 models
CTXM15R2V1B, CTXM15R5V1B, FTXM20R2V1B, FTXM20R5V1B, FTXM25R2V1B, FTXM25R5V1B, FTXM35R2V1B, FTXM35R5V1B, FTXM42R2V1B, FTXM42R5V1B, FTXM50R2V1B, FTXM60R2V1B, FTXM71R2V1B, ATXM20R2V1B, ATXM20R5V1B, ATXM25R2V1B, ATXM25R5V1B, ATXM35R2V1B, ATXM35R5V1B, ATXM50R2V1B, RXM20~71R(9), ARXM25~71R(9), FTXM20~71R, ATXM25~50R, FVXM25~50A
What this means
The refrigerant-liquid thermistor has an open or short circuit during compressor operation.
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.
See the official Daikin manualA deep link to the manufacturer's own PDF for full technical detail. We link to manuals, we never host them.