Error code
C4 Heat-exchanger temperature-sensor fault
Applies to 5 models
FTX20KV1B, FTX25KV1B, FTX35KV1B, FTX50KV1B, FTX60KV1B
What this means
The indoor heat-exchanger temperature sensor is faulty.
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.
Using Claude Code or Meta Muse? Connect HeatPump AI and ask it about C4.