Daikin L8-00 Fault Code: Causes, Fixes & Repair Costs
What does the Daikin L8-00 fault code mean?
The L8-00 fault code appears on Daikin heat pumps when the inverter detects that the compressor is drawing an abnormally high level of electrical current. The '00' suffix identifies this as a fault on outdoor unit number one. In plain terms, the system's inverter drive is protecting itself and the compressor by shutting down after sensing an overload condition — this could stem from a mechanical problem inside the compressor itself, an imbalance in the refrigerant circuit, a wiring issue, or a faulty inverter board sending incorrect readings. This is a serious outdoor unit fault and the heat pump should not be repeatedly restarted while this code is active, as doing so risks turning a repairable fault into a full compressor failure.
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
- Compressor mechanical overload or internal failure Common
The most frequently encountered root cause of L8 is the compressor itself struggling to turn or having partially seized. This can happen gradually as motor windings degrade over time, or more suddenly due to liquid refrigerant entering the compressor (known as slugging). When the compressor has to work harder than normal to overcome internal resistance, it draws excessive current and triggers the L8 protection.
- Refrigerant circuit imbalance — overcharge or blockage Common
If the refrigerant circuit contains too much refrigerant, or if there is a partial blockage somewhere in the system, the compressor is forced to work against abnormally high pressures. This extra mechanical load causes the current draw to spike into the territory that triggers L8. An overcharge is typically the result of previous refrigerant work carried out incorrectly.
- Compressor wiring disconnection or damaged coil Sometimes
A loose terminal, damaged wiring loom, or an open circuit within the compressor coil windings can cause the inverter to read an irregular current signature. The L8 alarm can be triggered not only by too much current but also by abnormal current patterns that the inverter interprets as an overload condition.
- Faulty inverter PCB Sometimes
The inverter printed circuit board is responsible for measuring and controlling the current delivered to the compressor. If the board itself is malfunctioning — due to age, a power surge, or component failure — it may report an overcurrent condition even when the compressor is operating within normal parameters. An engineer will need to test the board and its readings before condemning it.
- Insufficient power supply to the outdoor unit Rare
A supply voltage that is consistently lower than the unit's rated input, or a supply with poor phase balance on three-phase systems, can cause the compressor to draw disproportionately high current as it compensates. This is relatively uncommon on domestic installations but worth checking during diagnosis.
How to fix it
- Stop the unit immediately and do not attempt repeated resets DIY safe
Switch the heat pump off at the controller and leave it off. Repeatedly restarting the unit while an L8 fault is active places additional stress on the compressor and inverter, and risks escalating what might be a repairable fault into a full compressor write-off. One careful reset attempt after a few minutes is reasonable, but if the fault returns, leave the unit off.
- Check the outdoor unit isolator and the relevant MCB in the consumer unit DIY safe
Confirm that the outdoor unit's local isolator switch is in the on position and that no circuit breakers have tripped in your consumer unit. An unstable power supply can sometimes contribute to inverter faults. If a breaker has tripped, reset it once — but if it trips again, do not reset it further and contact an engineer.
- Clear any obstructions around the outdoor unit DIY safe
Ensure there are no leaves, debris, or accumulated ice blocking the intake or discharge grilles of the outdoor unit. Restricted airflow raises system pressures and can contribute to compressor overload. Keep at least the manufacturer's recommended clearance around all sides of the unit.
- Check system pressure at the filling loop or pressure gauge DIY safe
If your heat pump has a visible pressure gauge on the buffer vessel or pipework, check that it reads within the normal operating range (typically 1.0–2.0 bar when cold). Very low pressure in the heating circuit can affect system performance, though it is unlikely to be the direct cause of L8. Top up via the filling loop if the pressure is below 1.0 bar.
- Arrange for an F-Gas registered, MCS-certified heat pump engineer to carry out diagnosis heat pump engineer
Everything beyond the checks above requires a qualified engineer. They will inspect the compressor wiring and terminals for damage or disconnection, test the compressor motor windings, evaluate the inverter PCB and its current readings, and check the refrigerant charge weight. All refrigerant circuit work — including checking or adjusting the refrigerant charge — is legally restricted to F-Gas registered engineers.
- Inverter PCB replacement (engineer only) heat pump engineer
If testing confirms the inverter board is misreading current or has failed, the engineer will source and fit the correct replacement PCB for the unit's model and variant. Wiring polarity and model compatibility must be verified before the new board is powered up.
- Compressor replacement and full refrigerant recommission (engineer only) heat pump engineer
If the compressor has seized or its windings have broken down, the engineer will recover the existing refrigerant charge, remove the old compressor, braze in a new one, pressure-test the system, pull a full vacuum, and recharge with the correct weight of refrigerant. Post-repair, running pressures and temperatures should be monitored with a service tool to confirm the system is operating correctly.
Parts you may need
- Inverter PCB (outdoor unit) · from £380
- Compressor (model-dependent) · from £950
- Compressor wiring harness · from £65
- Refrigerant recharge (R32 or R410A, per kg) · from £55
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–£900, depending on the underlying cause.
Frequently asked questions
Can I just reset the L8-00 fault and carry on using my Daikin heat pump?
It is not advisable. A single reset to check whether the fault was a one-off transient is reasonable, but if L8 returns you should leave the unit off. Repeatedly restarting the heat pump while this fault is active puts additional mechanical and electrical stress on the compressor and inverter. What might be a £400–£500 inverter board repair can escalate into a compressor replacement costing well over £1,500 if the unit is run through the fault.
Why does L8-00 specifically need an F-Gas engineer and not just any heat pump engineer?
The most common root causes of L8 — refrigerant overcharge, circuit blockage, and anything that follows a compressor replacement — all involve the sealed refrigerant circuit. In the UK, handling, recovering, or recharging refrigerant is a legal requirement under F-Gas regulations and can only be carried out by an engineer holding a valid F-Gas handling certificate. Most MCS-certified heat pump engineers also hold F-Gas qualifications, but it is worth confirming this when you call.
How much does it typically cost to fix a Daikin L8-00 fault in the UK?
The cost depends on what the engineer finds. A wiring repair or straightforward refrigerant regas with a leak fix typically falls in the £350–£600 range. An inverter PCB replacement usually runs between £450 and £900 including parts and labour. If the compressor itself needs replacing, costs start at around £1,400 for a smaller split system and rise considerably for larger or multi-zone units. Your engineer should be able to give you a firm quote once they have diagnosed the root cause.
Could extreme cold weather be causing my Daikin to show L8-00?
Extreme low temperatures can raise the pressure differential that the compressor works against, which in turn increases current draw. In borderline cases this might contribute to an L8 trip. However, if the unit was previously operating fine through cold spells and L8 has appeared suddenly, weather alone is unlikely to be the sole cause. An engineer should still carry out a full diagnosis to rule out a compressor or refrigerant issue rather than attributing the fault purely to ambient conditions.