Daikin LC-00 Fault Code: Causes, Fixes & Repair Costs
What does the Daikin LC-00 fault code mean?
The LC-00 fault code indicates that the outdoor unit's main control PCB has lost reliable communication with the inverter PCB — the board responsible for varying the compressor's speed to deliver the right amount of heating or cooling output. Daikin's firmware monitors this data link continuously, and if a valid signal is not exchanged within a set time window, it triggers the LC-00 alarm and locks the system out to prevent damage. Because the 'L' prefix always denotes an outdoor-unit fault, the problem lies within the outdoor unit's electronics rather than the indoor unit or cylinder controller. The '00' sub-code is the base variant; on larger multi-zone systems you may occasionally see LC-14, LC-15, or LC-16, which point to specific inverter circuits, but they share the same root cause category.
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
- Loose or corroded wiring harness between PCBs Common
The ribbon cable or plug-in connectors linking the control PCB to the inverter PCB inside the outdoor unit can work loose over time due to vibration from the compressor and fan. Moisture ingress — common in outdoor units in the UK climate — can also cause pin corrosion that raises contact resistance enough to break the data signal. This is the most frequent root cause found by engineers attending LC-00 call-outs.
- Faulty inverter PCB Common
The inverter PCB itself can fail due to component degradation, moisture damage, power-surge events, or simply age. When the inverter board can no longer respond correctly to the control PCB's signals, the communication handshake fails and LC-00 is logged. PCB failure is more likely on units over five years old or those that have experienced repeated electrical transients.
- Faulty main control PCB Sometimes
Less often, it is the control PCB's own communication circuitry that fails rather than the inverter board. This can follow a power surge or lightning event, or simply be component end-of-life. An engineer will usually need to isolate which board is at fault before ordering parts.
- Electrical noise or interference Sometimes
Variable-frequency drives and inverter circuits are sensitive to electromagnetic interference. Nearby industrial equipment, poorly earthed wiring, or a failing noise-filter PCB within the outdoor unit can corrupt the data signal between boards without either PCB itself being defective. Resolving the interference source or replacing the noise-filter board often clears the fault.
- Failing or seized compressor Rare
The inverter PCB monitors compressor motor feedback. If the compressor is developing a winding fault or mechanical seizure, the abnormal electrical load can disrupt the inverter's operation to the point where PCB communication breaks down. This is a more serious and costly scenario and tends to be accompanied by other symptoms such as unusual noise from the outdoor unit.
- Incorrect or incompatible spare-part PCB installed Rare
If a PCB was replaced previously with a board of the wrong capacity rating or firmware version, the two boards may never communicate correctly, resulting in a persistent LC-00. This is only relevant where prior repair work has been carried out.
How to fix it
- Switch the heat pump off at the controller and isolate power at the outdoor unit's dedicated isolator switch. Wait at least 10 minutes, then restore power and restart normally. DIY safe
A brief power cycle clears temporary communication glitches caused by transient electrical noise or a momentary data-link dropout. Ten minutes is long enough for the inverter capacitors to fully discharge and the control firmware to reinitialise cleanly. If the fault clears and does not return within a heating cycle, monitor the system over the next 24 hours. If LC-00 reappears, move on to the next steps.
- Check the area around the outdoor unit for anything that could be causing electrical interference, and verify the unit's isolator and any MCB in the consumer unit have not tripped. DIY safe
Look for new electrical equipment installed nearby — large motors, welding equipment, or additional inverter-driven appliances — that may be introducing noise onto the supply. Also confirm the heat pump's dedicated MCB is firmly in the 'on' position and has not partially tripped. Do not open the outdoor unit casing.
- Visually inspect the exterior of the outdoor unit for signs of moisture ingress, pest damage to cabling, or obvious physical damage to the unit. DIY safe
Check that the unit's top grille and side panels are undamaged and seated correctly, as gaps allow wind-driven rain inside. Look for any external wiring entering the unit that appears chafed or compressed. Report these observations to the engineer — they help narrow down whether moisture or a wiring issue is the likely cause.
- Book an MCS-certified heat pump engineer to carry out a full diagnostic inspection of the outdoor unit's internal wiring and PCBs. heat pump engineer
The engineer will open the outdoor unit and check the harness connectors between the control PCB and the inverter PCB, looking for loose pins, corrosion, or damaged insulation. They will also test the noise-filter PCB and check for any capacity or firmware mismatch if a PCB has been replaced previously. High voltages are present inside the outdoor unit even shortly after isolation — this work must not be attempted by anyone without the appropriate training and equipment.
- Allow the engineer to replace whichever PCB (control board, inverter board, or noise-filter board) their diagnosis identifies as faulty. heat pump engineer
Genuine Daikin replacement boards are strongly recommended over third-party alternatives, as firmware compatibility is critical for correct PCB-to-PCB communication. Daikin's UK parts hub in Weybridge typically offers next-day delivery on common boards, so downtime is usually limited to one or two days once the faulty component is confirmed.
- If the engineer identifies compressor motor winding faults contributing to the LC-00, arrange compressor assessment and, if necessary, replacement. heat pump engineer
Compressor replacement is a major refrigerant-circuit job requiring an F-Gas registered engineer to recover and recharge refrigerant safely. On units over eight to ten years old, the engineer may advise comparing repair costs against a new heat pump, especially if both a PCB and compressor need replacing simultaneously.
Parts you may need
- Daikin inverter PCB (outdoor unit) · from £320
- Daikin main control PCB (outdoor unit) · from £290
- Noise filter PCB · from £130
- PCB-to-PCB wiring harness / connector set · from £45
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 £350–£850, depending on the underlying cause.
Frequently asked questions
Is LC-00 a serious fault — will my heat pump restart on its own?
LC-00 is a lockout fault, meaning the heat pump will not resume heating until the underlying issue is resolved and the error is cleared. A single power-cycle reset is always worth trying, but if the code returns after restart it indicates a genuine electronic fault inside the outdoor unit that needs an engineer. Leaving it unattended in winter risks your home losing heat, so it is worth booking a call-out promptly rather than waiting to see if it clears.
Can I fix Daikin LC-00 myself?
The only homeowner-safe steps are a power reset and a visual check around the outside of the outdoor unit. Everything else — opening the unit casing, testing PCB connectors, or replacing boards — involves high-voltage components and should only be carried out by a qualified engineer. Attempting DIY PCB work can also void any remaining manufacturer or installer warranty.
How much does it typically cost to repair a Daikin LC-00 fault in the UK?
Most LC-00 repairs fall in the range of £350 to £850 once you include the engineer's call-out, diagnosis, a replacement PCB, and labour. The exact figure depends on which board has failed and the specific Daikin model, as PCB prices vary considerably. In the less common situation where a compressor fault is also involved, costs can rise to £1,000 or more — if you are facing that scenario on an older unit, it is worth asking your engineer whether the economics of repair versus replacement make sense.
Could a power surge have caused my Daikin LC-00 fault?
Yes — a power surge or lightning-induced transient is a recognised cause of PCB communication failures, including LC-00. If the fault appeared immediately after a storm or a supply interruption, tell your engineer, as this helps them focus on surge damage to the boards rather than a gradual wiring or corrosion issue. It is also worth checking whether your home or heat pump installation has adequate surge protection on the incoming supply.