- Heat pumps
- Air-to-water heat pump
L3-00
Daikin Altherma 4 H F L3-00: outdoor switch box temperature high
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
On Daikin Altherma 4 H F units, L3-00 means an outdoor unit electrical box temperature rise problem triggered because the switch box temperature is too high, stopping the heat pump with a manual reset. Check outside temperature in [6.3], verify the outdoor unit is uncovered, and call your installer.
Safety first
Stop and check this first
- When carrying out an inspection on the switch box of the unit, always make sure the unit is disconnected from the mains, wait more than 10 minutes, and verify capacitor voltage is less than 50 V DC before touching electrical components: never open the outdoor switch box yourself.
- To prevent hazards due to inadvertent resetting of the thermal cut-out, power to this appliance must not be supplied through an external switching device such as a timer, or connected to a circuit that is regularly turned ON and OFF by the utility.
Safe checks you can perform
- Check [11] Malfunction history for companion L4 or L8 thermal protection codes
- Compare the outdoor temperature in [6.3] Sensors with Daikin operating limits
- Verify from outside that the outdoor unit is uncovered and surrounding space is clean
Leave these tasks to a qualified professional
- Do not attempt this professional task: Perform manual reset of L3-00 and monitor switch box temperature during [7.3] test run
- Do not attempt this professional task: Disconnect mains, verify capacitor voltage below 50 V DC, and inspect the outdoor switch box
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.
Perform manual reset of L3-00 and monitor switch box temperature during [7.3] test run
What they doAfter correcting the cause of the switch box temperature rise and reattaching all covers, the installer resets L3-00 manually and runs [7.3] Maintenance mode > Operation test run over a full load cycle to confirm switch box temperature remains stable.
They must show youthe [11] Malfunctioning screen and [11] Malfunction history free of L3-00 after the full load test run.
In writingthe manual reset timestamp, the duration and mode of the [7.3] test run, and confirmation that L3-00 did not recur.
Disconnect mains, verify capacitor voltage below 50 V DC, and inspect the outdoor switch box
What they doWith the unit disconnected from the mains for more than 10 minutes and main circuit capacitors measured below 50 V DC, the authorised technician opens the outdoor switch box, checks for loose power connections or heat discoloration on terminal strip X*M and boards A1P/A2P/A3P/A4P, and checks the switch box temperature reading per the Daikin service manual.
They must show youphotos of the open outdoor switch box terminals and the measured switch box temperature reading compared against the service manual.
In writingthe condition of the switch box terminals and boards, the sensor reading verified, and any corrective action or part reference replaced.
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 companion L4 or L8 thermal protection codes
- Who:
- You, reading the L3-00 history on the indoor touchscreen with advanced end user permission.
- How:
- Open [11] Malfunctioning to read the long description for L3-00, then check [11] Malfunction history to see whether L4 codes (inverter or fan radiation fin overheating) or L8 codes (thermal protection in the inverter PCB) occurred on the same day.
- Result that matters:
- Whether multiple outdoor electronic thermal protections triggered together or L3-00 appeared alone.
- If L4 or L8 codes appear alongside L3-00 in the history log, that points to genuine heat buildup across the outdoor unit power electronics and switch box.
- If L3-00 is logged alone during mild weather, that isolates the trigger to the switch box compartment or its temperature measurement for the technician to verify.
- Evidence to keep:
- Take a photo of the [11] Malfunctioning screen and the [11] Malfunction history list.
Do not reset L3-00 without finding the cause; Daikin warns that when a safety or thermal protection activates, you must find out why before resetting it.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Compare the outdoor temperature in [6.3] Sensors with Daikin operating limits
- Who:
- You, checking the indoor user interface menu [6] Information.
- How:
- Go to [6.3] Information > Sensors and [6.5] Information > Operation modes to read the outside temperature and active mode, and compare them with Daikin's outdoor ambient limits: -28~25°C in heating mode, 10~43°C in cooling mode, and up to 40°C for domestic hot water production.
- Result that matters:
- Whether the outdoor unit was operating outside its designed ambient temperature range when L3-00 tripped.
- If the outside temperature exceeded 25°C during heating, 40°C during domestic hot water, or 43°C during cooling, that indicates the unit was operating above its ambient design window.
- If the outside temperature was well within the published range (or cold) when L3-00 stopped the unit, that rules out extreme ambient weather and points to an internal switch box heat source or sensor fault.
- Evidence to keep:
- Photograph the [6.3] Sensors screen showing the outside temperature and note the active operation mode.
Never open the outdoor unit switch box cover to check internal heat yourself; high voltage and capacitor charge remain inside.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Verify from outside that the outdoor unit is uncovered and surrounding space is clean
- Who:
- You, inspecting the exterior of the outdoor unit without touching grilles or removing covers.
- How:
- Check that no objects or covers are placed on top of the outdoor unit, that the area around the unit is clean and not enclosed, and check [5.23] Emergency selection on the indoor screen for backup heating coverage.
- Result that matters:
- Ruling out external enclosures or objects trapping heat around the outdoor unit casing while keeping indoor comfort active.
- If objects were resting on top of the unit or enclosing the area around it, that points to restricted heat dissipation around the outdoor casing that you should clear from outside and report.
- If the outdoor unit is completely clear and unenclosed, that rules out external blockage and leaves diagnosis to the authorised installer inside the switch box.
- Evidence to keep:
- Save a photo of the outdoor unit exterior and the [5.23] Emergency selection setting.
Do not place objects on top of the unit or enclose the area around the outdoor unit, and keep circuit breakers ON so R290 protections stay active.
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 L3-00
- code erreur Daikin Altherma L3-00
- codice L3-00 pompa di calore Daikin
- código L3-00 bomba de calor Daikin
- Daikin Altherma error L3-00
- Daikin Altherma Fehler L3-00
- Daikin heat pump code L3-00
- Daikin L3-00
- Daikin Wärmepumpe Fehlercode L3-00
- défaut L3-00 pompe à chaleur Daikin
- error Daikin Altherma L3-00
- errore Daikin Altherma L3-00
What it means
In Daikin installer reference guide 4PEN773391-1C (Chapter 14, section 14.4.4, page 210), code L3-00 is defined as OU: Electrical box temperature rise problem with the trigger Switch box temperature is too high, stopping heat pump operation and requiring a manual reset. Unlike L4-00, L4-01, L4-06, and L4-07 (which monitor the inverter or fan radiation fins), L3-00 specifically monitors the temperature inside the outdoor unit electrical switch box compartment. Because high ambient heat, restricted exterior airflow, loose high-resistance power terminals in the switch box, or a faulty temperature sensor reading can all trigger L3-00, the code alone does not prove a specific board failed.
Warnings and stop conditions
- Highsource verified
When carrying out an inspection on the switch box of the unit, always make sure the unit is disconnected from the mains, wait more than 10 minutes, and verify capacitor voltage is less than 50 V DC before touching electrical components: never open the outdoor switch box yourself.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Mediumsource verified
To prevent hazards due to inadvertent resetting of the thermal cut-out, power to this appliance must not be supplied through an external switching device such as a timer, or connected to a circuit that is regularly turned ON and OFF by the utility.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Symptoms and causes
Probable causes · in order
- Actual overheating inside the outdoor unit electrical switch boxPossible
High ambient temperature, blocked ventilation around the outdoor unit casing, or heat generated by loose connections in the switch box raises the internal compartment temperature above the controller threshold.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
- Switch box temperature sensing abnormality on the outdoor unitPossible
If L3-00 triggers when the outdoor unit has just started in cool weather with no companion L4 or L8 thermal protection codes, the switch box temperature measurement itself may be out of calibration or faulty.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Virtual technician
Does L3-00 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
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