Error C4 on Daikin FTXF25D Mini-Split | Causes & Fix

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• Source: Official Daikin service manual
• Reviewed by: Geo Technical Editorial
• Published: March 15, 2026
• Updated: March 15, 2026

Safety notice: Start with user-safe checks only. Do not open sealed refrigerant systems, inspect gas-train components, or work on energized high-voltage parts unless you are qualified to service this appliance.

Error C4 on Daikin : Indoor coil sensor fault. Follow the troubleshooting steps below to diagnose and fix this mini-split issue. ## What Error Code C4 Means on a Daikin FTXF25D Error C4 on the Daikin FTXF25D indicates the indoor unit heat exchanger (coil) temperature sensor is faulty. The C4 sensor (thermistor) is mounted on the indoor coil and is used for freeze protection and temperature control. A faulty C4 sensor means the control board cannot safely monitor the coil temperature, and the system raises C4 to prevent a freeze event. The sensor is located on the indoor coil — typically accessible after removing the indoor unit casing. When C4 appears, the Daikin mini split pauses normal operation to protect internal components from potential damage. Not every C4 fault requires a professional engineer — many are resolved through careful inspection and routine maintenance. Work through each diagnostic step below in sequence, starting with the simplest check, to identify the root cause efficiently before considering part replacement or arranging a service call. ## Symptoms - C4 on indoor unit display

• System not cooling or heating
• Unit starts then immediately stops with C4 ## Common Causes - Indoor coil sensor fault ## Tools You May Need - digital multimeter
• Phillips screwdriver ## Step-by-Step Repair Guide | Step | Action | Result | |------|--------|--------| | 1 | Isolate the AC. Remove the indoor unit front panel. | Panel removed — continue to step 2 if the issue persists. | | 2 | Locate the C4 coil temperature thermistor (clipped to the coil fins). | Sensor located — continue to step 3 if the issue persists. | | 3 | Disconnect the thermistor connector. Test resistance at 25 °C: expect ~10 kΩ. | Resistance measured — continue to step 4 if the issue persists. | | 4 | Replace thermistor if OL or 0 Ω. | Thermistor replaced — continue to step 5 if the issue persists. | | 5 | Reassemble, restore power, and test cooling/heating. | C4 cleared — if the fault remains, contact a qualified technician. | ## Safety Precautions Isolate the AC at the circuit breaker before accessing the indoor coil. The coil fins are sharp — use gloves when handling the coil area. ## Estimated Repair Time and Difficulty Most mini split error code C4 faults can be assessed and addressed in 30–90 minutes using the steps above. The diagnostic process requires only basic tools: a multimeter and standard screwdrivers cover the majority of checks described here. If a replacement part is required, allow 1–5 working days for delivery. A trained technician with access to the correct diagnostic equipment will typically resolve this type of fault within a single service visit. ## When to Call a Technician Contact a Daikin authorised service technician if: the fault persists after following all the steps above; if PCB-level or refrigerant-circuit work is required; or if you are not comfortable working with electrical or mechanical components. When calling, have the full model number, the error code displayed, and a brief description of any sounds or symptoms you noticed before the fault appeared — this helps the technician prepare the correct parts and tools. ## Frequently Asked Questions Q: Is the C4 sensor the same as the room temperature sensor? No — C4 is the indoor coil temperature sensor (used for freeze protection). The room temperature sensor is a separate thermistor. Q: Can C4 appear without ice on the coil? Yes — C4 is a sensor fault, not necessarily a freeze event. The sensor may be faulty even if the coil looks normal. Q: Is C4 a common fault? C4 is not uncommon after several years of service. Condensation and vibration can weaken the thermistor leads over time. ### Is it safe to keep using my Daikin with error C4? If error C4 does not indicate an immediate safety hazard such as a gas leak, electrical short, or water flooding, you can continue limited use while monitoring the appliance. However, running the mini-split with an active error code increases the risk of further damage. Address the underlying issue as soon as possible. For high-severity errors, disconnect the appliance and contact a qualified technician. ### How much does it cost to fix error C4 on a Daikin ? Repair costs for error C4 on the Daikin mini-split depend on the root cause. DIY fixes such as cleaning filters, resetting the unit, or reconnecting loose wires cost nothing beyond basic tools. If a component replacement is needed, parts and labor from a certified technician are the main expenses. Contact a Daikin-authorized service provider for an accurate estimate based on your specific situation. ### What does error code C4 mean on a Daikin mini-split? Error code C4 on Daikin mini-split models indicates Indoor coil sensor fault. This error is detected by the appliance’s internal diagnostic system and displayed to alert the user that attention is needed. Refer to the troubleshooting steps above for guidance on resolving this issue. ### Is it safe to keep using my Daikin with error C4? If error C4 does not indicate an immediate safety hazard such as a gas leak, electrical short, or water flooding, you can continue limited use while monitoring the appliance. However, running the mini-split with an active error code increases the risk of further damage. Address the underlying issue as soon as possible. For high-severity errors, disconnect the appliance and contact a qualified technician. ### How much does it cost to fix error C4 on a Daikin ? Repair costs for error C4 on the Daikin mini-split depend on the root cause. DIY fixes such as cleaning filters, resetting the unit, or reconnecting loose wires cost nothing beyond basic tools. If a component replacement is needed, parts and labor from a certified technician are the main expenses. Contact a Daikin-authorized service provider for an accurate estimate based on your specific situation. ### What does error code C4 mean on a Daikin mini-split? Error code C4 on Daikin mini-split models indicates Indoor coil sensor fault. This error is detected by the appliance’s internal diagnostic system and displayed to alert the user that attention is needed. Refer to the troubleshooting steps above for guidance on resolving this issue.