- Heat pumps
- Air-to-water heat pump
L4-06
Daikin Altherma 4 H F L4-06: fan 1 radiation fin overheating
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
Daikin Altherma 4 H F code L4-06 stops the heat pump on a manual reset when the outdoor unit detects overheating on the fan 1 radiation fin. Check menu [11] Malfunctioning for companion sensor code P4-02, record the outside reading in [6.3], and call your installer.
Safety first
Stop and check this first
- Never shunt thermal safety devices or connect the heat pump to an external timer or utility-switched circuit; inadvertent resetting of a thermal cut-out creates a hazard and can damage the outdoor inverter assembly.
- Do not open the outdoor unit or remove its switch box cover yourself. Before touching any internal electrical parts, a qualified technician must turn off all power supplies for more than 10 minutes and measure less than 50 V DC on the main circuit capacitors.
Safe checks you can perform
- Inspect menu [11] Malfunctioning and Malfunction history for P4-02 alongside L4-06
- Read the outside temperature in [6.3] Information > Sensors and note the active mode
- Check exterior clearance around the outdoor unit without touching the aluminium fins
- Check [5.23] Emergency selection rather than resetting L4-06 manually
Leave these tasks to a qualified professional
- Do not attempt this professional task: Measure fan 1 fin thermistor resistance and inspect the fan 1 radiation fin after capacitor discharge
- Do not attempt this professional task: Resolve the overheating cause, perform the manual reset, and verify fan 1 fin temperature under load
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.
Measure fan 1 fin thermistor resistance and inspect the fan 1 radiation fin after capacitor discharge
What they doHave a Daikin certified technician disconnect all power supplies for more than 10 minutes, confirm less than 50 V DC across the main circuit capacitors, and inspect the fan 1 radiation fin, thermal contact, and fan 1 fin temperature sensor connector.
They must show youthe multimeter reading below 50 V DC before switch box access and the measured resistance of the fan 1 fin thermistor compared against the service manual table.
In writingthe residual capacitor voltage in V DC, the fan 1 fin thermistor resistance in ohms at ambient temperature, and the physical condition of the fan 1 radiation fin.
Resolve the overheating cause, perform the manual reset, and verify fan 1 fin temperature under load
What they doOnce the technician corrects any fin fouling, sensor fault, or inverter board issue per the service manual, they must perform the manual reset for L4-06 and monitor live fan 1 fin temperature through a full heating or hot water cycle.
They must show youthe live fan 1 radiation fin temperature during test operation and the [11] Malfunction history screen free of new L4-06 or P4-02 entries.
In writingthe root cause identified for L4-06, the part number of any replaced sensor or PCB, and the peak fan 1 fin temperature recorded during the post-repair 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.
Inspect menu [11] Malfunctioning and Malfunction history for P4-02 alongside L4-06
- Who:
- You as the homeowner at the indoor unit touchscreen with advanced end user permission enabled.
- How:
- Open [11] Malfunctioning, tap L4-06 to read the long error description, and open [11]: Malfunction history to see whether P4-02, L1-55, or L3-00 logged near the same timestamp.
- Result that matters:
- Whether L4-06 occurred as a standalone thermal trip or together with a fan 1 fin thermistor error.
- If P4-02 appears in the malfunction history alongside L4-06, that points to a fan 1 fin temperature sensor or harness fault rather than genuine heatsink overheating.
- If L4-06 is the only code logged, that rules out an open sensor fault and indicates the controller measured excessive temperature on the fan 1 radiation fin.
- Evidence to keep:
- Take a clear photo of the [11] Malfunctioning long description and the timestamped malfunction history list.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Read the outside temperature in [6.3] Information > Sensors and note the active mode
- Who:
- You reading the indoor user interface information menu right after L4-06 stops the unit.
- How:
- Navigate to [6.3] Information > Sensors to read the outside and water temperatures, and note whether the system was running space heating, cooling, or domestic hot water.
- Result that matters:
- How the outside temperature compares with Daikin's rated outdoor envelope (-28~25°C in heating, 10~43°C in cooling, and up to 40°C for domestic hot water).
- If the outside sensor reading is above 40°C during hot water heat-up or 43°C during cooling, that indicates ambient operating conditions contributed to the L4-06 trip.
- If the outside temperature is well inside the rated window, that rules out extreme weather and isolates the problem to local airflow or the fan 1 radiation fin assembly.
- Evidence to keep:
- Record the exact outside temperature value from [6.3] and the active operating mode when L4-06 appeared.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Check exterior clearance around the outdoor unit without touching the aluminium fins
- Who:
- You performing a visual check from outside the outdoor unit casing.
- How:
- Verify from a safe distance that no objects sit on top of the outdoor unit and that leaves, snow, or covers do not block the ventilation openings.
- Result that matters:
- Whether air can circulate freely around the outdoor unit casing and fan 1 discharge path.
- If a tarp, objects on the top panel, or foliage blocked the ventilation openings, removing the exterior obstacle confirms an airflow restriction that could overheat the fan 1 fin.
- If the area around the outdoor unit is completely clear and well ventilated, that rules out an external blockage and points to internal heatsink cooling or sensing.
- Evidence to keep:
- Save a photo of the outdoor unit and its surrounding clearance to show the visiting technician.
Never open the outdoor unit casing or touch the air inlet or aluminium fins; internal parts carry mains voltage and R290 refrigerant.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Check [5.23] Emergency selection rather than resetting L4-06 manually
- Who:
- You at the indoor user interface while waiting for your Daikin installer.
- How:
- Leave the L4-06 manual reset untouched, check [5.23] Settings > Emergency selection to see if the backup heater can take over heating and hot water, and look up your installer phone number in [6.2] Dealer information.
- Result that matters:
- Whether emergency backup heating is active so household hot water and heating continue safely while the outdoor unit stays off.
- If the emergency selection menu allows backup heater takeover, that confirms the indoor electrical heater can maintain comfort until the technician diagnoses L4-06.
- If the backup heater does not take over and indoor temperature drops, that indicates manual acknowledgment in [5.30] or prompt service via [6.2] is required.
- Evidence to keep:
- Note the current setting in [5.23] Emergency selection and the dealer contact details from [6.2].
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 L4-06
- code erreur Daikin Altherma L4-06
- codice L4-06 pompa di calore Daikin
- código L4-06 bomba de calor Daikin
- Daikin Altherma error L4-06
- Daikin Altherma Fehler L4-06
- Daikin heat pump code L4-06
- Daikin L4-06
- Daikin Wärmepumpe Fehlercode L4-06
- défaut L4-06 pompe à chaleur Daikin
- error Daikin Altherma L4-06
- errore Daikin Altherma L4-06
What it means
In section 14.4.4 of the Daikin Altherma 4 H F installer reference guide (4PEN773391-1C), code L4-06 is classified under OU: Malfunction of inverter radiating fin temperature rise with the specific trigger Overheating of fan 1 radiation fin. When tripped, the heat pump stops operating and requires a manual reset. Daikin separates fan 1 fin overheating (L4-06) from fan 2 fin overheating (L4-07) and main inverter fin overheating (L4-00, L4-01), while assigning P4-02 to the fan 1 fin temperature sensor itself. Consequently, L4-06 alone does not prove the inverter PCB or fan 1 module has failed.
Warnings and stop conditions
- Mediumsource verified
Never shunt thermal safety devices or connect the heat pump to an external timer or utility-switched circuit; inadvertent resetting of a thermal cut-out creates a hazard and can damage the outdoor inverter assembly.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Highsource verified
Do not open the outdoor unit or remove its switch box cover yourself. Before touching any internal electrical parts, a qualified technician must turn off all power supplies for more than 10 minutes and measure less than 50 V DC on the main circuit capacitors.
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
- Actual thermal rise on the fan 1 radiation fin during outdoor operationCommon
Blocked airflow around the outdoor heat exchanger or heavy thermal load near the ambient ceiling (up to 43°C in cooling or 40°C in domestic hot water) pushes the fan 1 heatsink past its temperature threshold.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
- False high-temperature reading from the fan 1 fin thermistor (P4-02 path)Possible
A loose connector or resistance drift on the fan 1 fin temperature sensor causes the outdoor controller to register overheating on the fan 1 radiation fin even when heatsink temperature is normal.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Elevated switch box heat or fan 1 driver stress on the inverter assemblyLess common
Poor heat transfer at the fan 1 radiation fin or an accompanying electrical box temperature rise (L3-00) or fan driver error (L1-55) drives the local heatsink temperature above its limit.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Virtual technician
Does L4-06 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
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