Daikin C4 fault code

What it means

Indoor heat-exchanger (liquid pipe) thermistor fault

The indoor coil sensor reads open or short circuit.

Safety: Safe isolation before disconnecting sensors or working on the PCB.

UK models this code applies to

From the Daikin service literature we hold (Daikin CTXM/FTXM-M operation manual 3PEN393186-10J, malfunction-code table (remote self-diagnosis)) — not a scraped list.

Now the harder half: proving what caused it

C4 names a symptom, not a root cause. In the app, the same code opens a guided investigation: what to measure first, the expected values for your exact model, and an honest verdict — including “nothing in this machine is broken” when that's what the readings say.