- Heat pumps
- Air-to-water heat pump
L8-00
Daikin Altherma 4 H F L8-00: inverter PCB thermal protection
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
Daikin Altherma 4 H F error L8-00 means a thermal protection in the outdoor inverter PCB stopped the heat pump on a manual reset. Check [11] Malfunction history for specific L8 or L4 subcodes, verify that outdoor airflow is clear, and call your installer.
Safety first
Stop and check this first
- To prevent hazards from inadvertent resetting of the thermal cut-out, power to this heat pump must never be supplied through an external switching device such as a timer or connected to a circuit regularly turned ON and OFF by the utility.
- Never open the outdoor switch box cover or touch internal parts yourself. A technician must turn off all power supplies, wait more than 10 minutes, and verify less than 50 V DC on the main circuit capacitors before touching electrical components.
Safe checks you can perform
- Check [11] Malfunction history for specific L8-01 through L8-14, L4, or L3 codes
- Inspect the outdoor unit exterior for blocked ventilation openings without touching fins
- Verify that the heat pump is not on an external timer or regularly switched utility circuit
Leave these tasks to a qualified professional
- Do not attempt this professional task: Verify dedicated power circuit, inverter-compatible RCD, and terminal tightness
- Do not attempt this professional task: Diagnose the inverter PCB thermal protection branch and run a loaded verification test
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Verify dedicated power circuit, inverter-compatible RCD, and terminal tightness
What they doHave an authorised electrician or Daikin technician disconnect the mains, verify that the unit uses a dedicated power circuit without external timers and an inverter-compatible earth leakage protector, and inspect switch box terminals after waiting more than 10 minutes and confirming less than 50 V DC.
They must show youthe sub-50 V DC capacitor measurement after the 10-minute wait and the dedicated breaker and inverter-compatible earth leakage protector ratings.
In writingthe measured residual DC voltage (V DC), incoming supply voltage (V AC), breaker/RCD specifications, and terminal inspection results.
Diagnose the inverter PCB thermal protection branch and run a loaded verification test
What they doFollowing the service manual for L8-00 and any companion L8 subcodes, the technician must test the inverter PCB cooling path and compressor load, perform the manual reset once the cause is resolved, and verify stable operation under heating or hot water demand.
They must show youthe post-reset test run under load and the [11] Malfunction history screen confirming L8-00 does not return.
In writingthe exact thermal trigger found, the reference of any replaced inverter PCB or component, and the operating mode and duration of the load test.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Check [11] Malfunction history for specific L8-01 through L8-14, L4, or L3 codes
- Who:
- You at the indoor unit touchscreen with advanced end user permission active.
- How:
- Open [11] Malfunctioning to view the long help text for L8-00, then open [11]: Malfunction history to check whether L8-01, L8-02, L8-03, L8-04, L8-05, L8-14, L3-00, or L4-00 also appeared.
- Result that matters:
- Identifying the specific thermal, step-out, overcurrent, or lightning subcode accompanying general code L8-00.
- If L8-04 appears near L8-00 after a thunderstorm, that points to lightning detection rather than a mechanical overload.
- If L8-01, L8-02, L8-05, L3-00, or L4-00 appear in the history, that indicates sustained thermal or current stress inside the outdoor inverter assembly.
- Evidence to keep:
- Take a photo of the [11]: Malfunction history screen showing all L-series codes and their timestamps.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Inspect the outdoor unit exterior for blocked ventilation openings without touching fins
- Who:
- You checking the outdoor unit from outside without opening covers or touching the aluminium fins.
- How:
- Look around the outdoor unit to ensure sufficient space exists for air circulation, nothing is placed on top of the cabinet, and no leaves, snow, or tarps block the ventilation openings.
- Result that matters:
- Confirming unobstructed outdoor airflow so heat can escape the inverter switch box and radiating fins.
- If debris, snow, or a cover was restricting the ventilation openings, clearing the exterior area confirms an airflow issue that you should report to the installer.
- If the outdoor unit has clean, open clearance on all sides, that rules out external suffocation and points to electrical load or internal inverter PCB cooling.
- Evidence to keep:
- Keep a photo of the outdoor unit installation site and its ventilation clearances.
Do not touch the air inlet or aluminium fins of the outdoor unit, and never open the outdoor unit casing.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Verify that the heat pump is not on an external timer or regularly switched utility circuit
- Who:
- You reviewing your household installation setup and user interface without opening electrical panels.
- How:
- Check your installation documentation or ask your installer whether the heat pump runs on a dedicated power circuit without an external timer or frequent ON/OFF utility switching, and leave the unit circuit breakers ON.
- Result that matters:
- Compliance with Daikin's warning in section 14.2 against external switching devices that cause inadvertent thermal cut-out resets.
- If the appliance is wired through an external timer or non-dedicated circuit, that points to an improper power supply setup that an authorised electrician must correct.
- If the unit is on a dedicated power circuit with no external switching device, that rules out supply switching and isolates the diagnosis to the outdoor inverter stage.
- Evidence to keep:
- Note how the heat pump power circuit is configured and save the installer contact from [6.2] Dealer information.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Heat pumps
- Brand
- Daikin
- Product type
- Air-to-water heat pump
Known code variants
- Altherma 4 H F L8-00
- code erreur Daikin Altherma L8-00
- codice L8-00 pompa di calore Daikin
- código L8-00 bomba de calor Daikin
- Daikin Altherma error L8-00
- Daikin Altherma Fehler L8-00
- Daikin heat pump code L8-00
- Daikin L8-00
- Daikin Wärmepumpe Fehlercode L8-00
- défaut L8-00 pompe à chaleur Daikin
- error Daikin Altherma L8-00
- errore Daikin Altherma L8-00
What it means
In section 14.4.4 of the Daikin Altherma 4 H F installer reference guide (4PEN773391-1C), code L8-00 is defined as Malfunction triggered by a thermal protection in the inverter PCB with the trigger Malfunction by thermal protection inverter PCB. The heat pump stops and needs a manual reset. L8-00 is the general head code of a family where L8-01 and L8-02 denote electronic thermal 1 and 2, L8-03 and L8-14 denote step-out or speed reduction, L8-04 denotes lightning detection, and L8-05 denotes time-limited overcurrent. Therefore, L8-00 alone does not prove the inverter PCB is defective.
Warnings and stop conditions
- Highsource verified
To prevent hazards from inadvertent resetting of the thermal cut-out, power to this heat pump must never be supplied through an external switching device such as a timer or connected to a circuit regularly turned ON and OFF by the utility.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Highsource verified
Never open the outdoor switch box cover or touch internal parts yourself. A technician must turn off all power supplies, wait more than 10 minutes, and verify less than 50 V DC on the main circuit capacitors before touching electrical components.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Symptoms and causes
Probable causes · in order
- Inverter electronic thermal trip or time-limited overcurrent under heavy loadCommon
Sustained high compressor current or speed step-out (tracked in sibling codes L8-01, L8-02, L8-03, L8-05, and L8-14) heats the inverter power stage until its thermal protection trips.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Restricted outdoor unit ventilation or elevated switch box and heatsink temperaturePossible
Blocked ventilation openings around the outdoor unit or high internal temperatures (associated with L3-00 switch box heat or L4-00/L4-01 inverter fin overheating) trigger the inverter PCB thermal cut-out.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
- Improper switched power supply, shared circuit, or lightning transientPossible
Supplying the unit through an external switching timer or shared circuit (prohibited in sections 2.1.5 and 14.2) or a lightning disturbance (related to L8-04) causes abnormal thermal protection activation on the inverter PCB.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Internal thermal sensing or hardware failure on the outdoor inverter PCBLess common
When airflow, power supply, and compressor load are verified normal yet L8-00 recurs after a professional reset, the thermal protection circuit on the inverter PCB itself may be faulty.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Virtual technician
Does L8-00 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Daikin Europe N.V. · 2026 · official_doc
Was this entry useful?