Daikin CJ-02 Fault Code: Causes, Fixes & Repair Costs
What does the Daikin CJ-02 fault code mean?
The CJ-02 fault code on Daikin heat pump systems points to an abnormality with the room temperature thermistor built into the remote controller. This small sensing component continuously measures the ambient temperature near the controller and feeds that data to the heat pump's control system. When the unit detects that this sensor has gone open-circuit or short-circuit during operation, it logs a CJ fault. The '02' suffix identifies the specific sub-code variant within Daikin's diagnostic framework, but the underlying fault definition remains consistent across Daikin's residential and light-commercial heat pump range. Because the affected component is in the controller rather than the heat pump itself, this is generally one of the less serious fault codes — the refrigerant circuit and compressor are unaffected — and the system can usually continue to operate for a short period while a repair is arranged.
General guidance only — not a substitute for professional advice, and not certified by an heat pump engineer. Always have your specific appliance assessed by a qualified professional. Any heat pump work must be carried out by an MCS-certified heat pump engineer. If you notice a refrigerant leak, a burning smell or water leaking from the unit, switch it off at the isolator and call an MCS-certified heat pump engineer. Refrigerant work must be carried out by an F-Gas registered engineer.
Common causes
- Failed remote controller thermistor Common
The thermistor itself — a small resistive sensor embedded in the remote controller handset or wall-mounted pad — has degraded or failed outright. Over time, heat cycling, humidity and general wear can cause the sensor's resistance to drift outside acceptable limits or break the circuit entirely. This is the most frequent root cause of a CJ-02 code.
- Defective remote controller PCB Sometimes
If the thermistor tests within its expected resistance range (approximately 10–12 kΩ at 25 °C), the fault may lie with the printed circuit board inside the remote controller rather than the sensor component itself. A damaged solder joint, failed capacitor or corroded trace on the controller PCB can produce exactly the same symptom.
- Electrical noise or interference Rare
Strong electromagnetic interference from nearby equipment — such as inverter drives, large motors or poorly earthed appliances — can occasionally corrupt the signal from the controller thermistor, causing the heat pump to misread it as a fault. This tends to be intermittent and is more likely in commercial settings with dense electrical infrastructure nearby.
How to fix it
- Check for any obvious issues around the remote controller DIY safe
Inspect the wall-mounted controller or handheld remote for physical damage, moisture ingress, or anything that may have been knocked. Ensure it has not been exposed to direct sunlight or a localised heat source (such as a nearby lamp or radiator) that could affect the sensor reading. Remove any obstructions and make sure the controller has good airflow around it.
- Attempt a controller reset DIY safe
On most Daikin systems, you can clear the stored fault record by pressing and holding the ON/OFF button for four seconds or longer while the unit is in inspection/diagnostic mode. Refer to your specific model's user guide for the precise sequence. Once reset, allow the system to run for at least 30 minutes and check whether the CJ-02 code returns. If it clears and stays clear, the fault may have been a transient event caused by electrical noise.
- Check the system is not losing power intermittently DIY safe
Locate the consumer unit (fuse board) and confirm that the MCB or fuse protecting the heat pump circuit has not tripped. A momentary power interruption can sometimes generate false controller errors. If you find a tripped MCB, switch it fully off then back on, restart the unit and monitor for the fault reappearing.
- Test the thermistor resistance — engineer task heat pump engineer
A qualified engineer will disconnect the thermistor from the controller PCB and measure its resistance with a multimeter. The expected value is in the region of 10–12 kΩ at 25 °C. A reading significantly above or below this range confirms sensor failure. This step involves working inside the controller electronics and should not be attempted by a homeowner.
- Replace the remote controller or thermistor — engineer task heat pump engineer
If the thermistor is confirmed faulty, the engineer will replace either the sensor component alone or the entire remote controller unit, depending on parts availability and cost. In many cases, replacing the complete controller is more practical and reliable than sourcing just the thermistor. No refrigerant circuit work is required for this repair.
- Investigate and mitigate electrical noise if fault persists — engineer task heat pump engineer
Where both the thermistor and PCB test as serviceable, the engineer will assess the installation environment for sources of electromagnetic interference and may recommend shielding or routing changes to the controller wiring. This is an uncommon scenario but worth investigating if the fault is intermittent and repeatedly clears on reset.
- Call an MCS-certified heat pump engineer heat pump engineer
If the reset does not resolve the CJ-02 code, or if it returns within a short time, arrange a visit from an MCS-certified heat pump engineer. This fault does not involve the sealed refrigerant circuit, so F-Gas registration is not required for the repair itself — however, an experienced Daikin-trained engineer will be able to diagnose and resolve the fault efficiently and ensure the controller is correctly configured after replacement.
Parts you may need
- Daikin remote controller (BRC series wall-mounted pad) · from £95
- Remote controller thermistor sensor · from £18
- Remote controller PCB (internal circuit board) · from £75
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £180–£350, depending on the underlying cause.
Frequently asked questions
Is it safe to keep running my Daikin heat pump with a CJ-02 fault?
In most cases, yes — for a short period. The CJ-02 fault relates to the room temperature sensor in the remote controller, not the compressor, refrigerant circuit or any safety-critical component. Your heat pump can typically continue to provide heating or cooling while you wait for an engineer. However, because the unit may not be reading room temperature accurately, it might not control output as efficiently as normal. We'd recommend arranging a repair within a few days rather than running indefinitely on a fault.
Can I fix the CJ-02 fault myself?
The one thing you can safely try is a controller reset — press and hold the ON/OFF button for around four seconds while the fault code is displayed. If this clears the code and it does not return, no further action may be needed. Beyond that, diagnosing and replacing the thermistor or controller PCB involves working inside the electronic components of the remote controller and should be left to a qualified engineer. There is no refrigerant or high-pressure work involved, so this is not an F-Gas job, but it does require proper diagnostic equipment.
How much does it cost to fix a CJ-02 fault on a Daikin heat pump in the UK?
Most homeowners pay in the region of £180–£350 all-in, which typically covers an engineer call-out, thermistor testing, and replacement of the remote controller or sensor. If the fault turns out to be a defective controller PCB that needs sourcing separately, costs can edge toward the higher end of that range. A full PCB replacement can cost £450–£900 in more complex cases, but this is less common for a CJ-02 specifically. The good news is that this fault does not involve any part of the main heat pump unit, so it remains one of the more affordable Daikin fault codes to resolve.
Will my Daikin warranty cover a CJ-02 fault?
It may do. Daikin's standard residential warranty covers manufacturer defects on parts for three years from installation. If the thermistor or controller PCB has failed within that period and the failure is not due to accidental damage or misuse, a warranty claim is reasonable. However, Daikin typically requires evidence of annual servicing by an appropriately qualified engineer — without service records, warranty claims are often declined. Check your warranty documentation and contact your installer or Daikin's UK support line to confirm your eligibility before commissioning a chargeable repair.