Daikin: Indoor Thermistor Fault

What this fault means

An indoor room or coil thermistor is reading out of range, so the system cannot control capacity properly — typically a C-series code on Daikin units.

Likely causes

• Failed or disconnected thermistor
• Damaged sensor wiring
• Indoor control board fault

What you can safely check

• Replace a dirty air filter — restricted airflow causes a surprising share of furnace faults.
• Confirm registers and the outdoor unit are clear of snow, leaves and debris.
• Cycle power at the switch once and let the system retry.

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